diff --git a/11_Day/11_function.md b/11_Day/11_function.md
index c9d20d1..28de92c 100644
--- a/11_Day/11_function.md
+++ b/11_Day/11_function.md
@@ -22,67 +22,68 @@
 - [📘 Day 11](#%f0%9f%93%98-day-11)
   - [Functions](#functions)
     - [Defining a Function](#defining-a-function)
-    - [Declaring and calling a function](#declaring-and-calling-a-function)
-    - [Function without parameters](#function-without-parameters)
-    - [Function returning value](#function-returning-value)
-    - [Function with parameters](#function-with-parameters)
-    - [Passing arguments with key and value](#passing-arguments-with-key-and-value)
-    - [Returning a value from a function](#returning-a-value-from-a-function)
-    - [Function with default parameters](#function-with-default-parameters)
-    - [Arbitrary number of arguments](#arbitrary-number-of-arguments)
-    - [Default and arbitrary number of parameters in function](#default-and-arbitrary-number-of-parameters-in-function)
-    - [Function as parameter of other function](#function-as-parameter-of-other-function)
+    - [Declaring and Calling a Function](#declaring-and-calling-a-function)
+    - [Function without Parameters](#function-without-parameters)
+    - [Function Returning a Value - Part 1](#function-returning-a-value---part-1)
+    - [Function with Parameters](#function-with-parameters)
+    - [Passing Arguments with Key and Value](#passing-arguments-with-key-and-value)
+    - [Function Returning a Value - Part 2](#function-returning-a-value---part-2)
+    - [Function with Default Parameters](#function-with-default-parameters)
+    - [Arbitrary Number of Arguments](#arbitrary-number-of-arguments)
+    - [Default and Arbitrary Number of Parameters in Functions](#default-and-arbitrary-number-of-parameters-in-functions)
+    - [Function as a Parameter of Another Function](#function-as-a-parameter-of-another-function)
   - [💻 Exercises: Day 11](#%f0%9f%92%bb-exercises-day-11)
 
 # 📘 Day 11
 
 ## Functions
 
-So far we have seen many builtin python functions. In this section, we will focus on custom functions. What is a function? Before we start making functions, lets understand what function is and why we need function?
+So far we have seen many built-in python functions. In this section, we will focus on custom functions. What is a function? Before we start making functions, lets learn what a function is and why we need them?
 
 ### Defining a Function
 
-A function is a reusable block of code or programming statements designed to perform a certain task. To define a function, Python provides the _def_ keyword. The following is the syntax of defining a function. The function block of code only executed only if we call the function.
+A function is a reusable block of code or programming statements designed to perform a certain task. To define a function, Python provides the _def_ keyword. The following is the syntax for defining a function. The function block of code is executed only if we call it.
 
-### Declaring and calling a function
+### Declaring and Calling a Function
 
-When we make a function we call it declaring a function. When we start using the function we call it calling or invoking a function. Function can be declared with or without a parameter.
+When we make a function we call it declaring a function. When we start using the it we call it calling or invoking a function. Function can be declared with or without parameters.
 
 ```py
-  # syntax
-  # Declaring a function
-  def function_name():
+# syntax
+# Declaring a function
+def function_name():
     codes
     codes
-  # Calling function
-  function_name()
+# Calling a function
+function_name()
 ```
 
-### Function without parameters
+### Function without Parameters
+
+Function can be declared without parameters.
 
-Function can be declared without a parameter.
 **Example:**
 
 ```py
-  def generate_full_name ():
-      first_name = 'Asabeneh'
-      last_name = 'Yetayeh'
-      space = ' '
-      full_name = first_name + space + last_name
-      print(full_name)
-  generate_full_name () # calling a function
+def generate_full_name ():
+    first_name = 'Asabeneh'
+    last_name = 'Yetayeh'
+    space = ' '
+    full_name = first_name + space + last_name
+    print(full_name)
+generate_full_name () # calling a function
 
-  def add_two_numbers ():
-      num_one = 2
-      num_two = 3
-      total = num_one + num_two
-      print(total)
-  add_two_numbers()
+def add_two_numbers ():
+    num_one = 2
+    num_two = 3
+    total = num_one + num_two
+    print(total)
+add_two_numbers()
 ```
 
-### Function returning value
+### Function Returning a Value - Part 1
 
-Function can also return values, if a function does not return values the value of the function is None. Lets rewrite the above functions using return. From now on, we return value to a function instead of printing it.
+Function can also return values, if a function does not return any, the value of the function is None. Lets rewrite the above functions using return. From now on, we get a value when calling the function, instead of printing it.
 
 ```py
 def generate_full_name ():
@@ -101,7 +102,7 @@ def add_two_numbers ():
 print(add_two_numbers())
 ```
 
-### Function with parameters
+### Function with Parameters
 
 In a function we can pass different data types(number, string, boolean, list, tuple, dictionary or set) as a parameter
 
@@ -150,7 +151,7 @@ sum_of_numbers(10) # 55
 sum_of_numbers(100) # 5050
 ```
 
-- Two Parameter: A function may or may not have a parameter or parameters. A function may have two or more parameters. If our function takes parameters we should call our function with arguments. Let's see function with two parameters:
+- Two Parameter: A function may or may not have a parameter or parameters. A function may have two or more parameters. If our function takes parameters we should call it with arguments. Let's check a function with two parameters:
 
 ```py
   # syntax
@@ -165,189 +166,189 @@ sum_of_numbers(100) # 5050
 **Example:**
 
 ```py
-  def generate_full_name (first_name, last_name):
-      space = ' '
+def generate_full_name (first_name, last_name):
+    space = ' '
       full_name = first_name + space + last_name
       return full_name
-  print('Full Name: ', generate_full_name('Asabeneh','Yetayeh'))
+print('Full Name: ', generate_full_name('Asabeneh','Yetayeh'))
 
-  def sum_two_numbers (num_one, num_two):
-      sum = num_one + num_two
-      return sum
-  print('Sum of two numbers: ', sum_two_numbers(1, 9))
+def sum_two_numbers (num_one, num_two):
+    sum = num_one + num_two
+    return sum
+print('Sum of two numbers: ', sum_two_numbers(1, 9))
 
-  def calculate_age (current_year, birth_year):
-      age = current_year - birth_year
-      return age;
+def calculate_age (current_year, birth_year):
+    age = current_year - birth_year
+    return age;
 
-  print('Age: ', calculate_age(2019, 1819))
+print('Age: ', calculate_age(2019, 1819))
 
-  def weight_of_object (mass, gravity):
-      weight = str(mass * gravity)+ ' N' # the value has to be changed to string first
-      return weight
-  print('Weight of an object in Newton: ', weight_of_object(100, 9.81))
+def weight_of_object (mass, gravity):
+    weight = str(mass * gravity)+ ' N' # the value has to be changed to a string first
+    return weight
+print('Weight of an object in Newtons: ', weight_of_object(100, 9.81))
 ```
 
-### Passing arguments with key and value
+### Passing Arguments with Key and Value
 
 If we pass the arguments with key and value, the order of the arguments does not matter.
 
 ```py
-  # syntax
-  # Declaring a function
-  def function_name(para1, para2):
+# syntax
+# Declaring a function
+def function_name(para1, para2):
     codes
     codes
-  # Calling function
-  function_name(para1='John', para2='Doe') # the order of argument now does not matter
+# Calling function
+function_name(para1='John', para2='Doe') # the order of arguments does not matter here
 ```
 
 **Example:**
 
 ```py
-  def print_fullname(firstname, lastname):
-        space = ' '
-        full_name = firstname  + space + lastname
-        print(full_name)
-  print_fullname(firstname='Asabeneh', lastname='Yetayeh')
+def print_fullname(firstname, lastname):
+    space = ' '
+    full_name = firstname  + space + lastname
+    print(full_name)
+print_fullname(firstname='Asabeneh', lastname='Yetayeh')
 
-  def add_two_numbers (num1, num2):
+def add_two_numbers (num1, num2):
     total = num1 + num2
     print(total)
-  add_two_numbers(num2=3, num1=2) # Order does not matter
+add_two_numbers(num2=3, num1=2) # Order does not matter
 ```
 
-### Returning a value from a function
+### Function Returning a Value - Part 2
 
-If we do not return a value from a function, then our function is returning _None_ by default. To return a value from a function we use the key word _return_ followed by the data type we are returning. We can return any kind of data types from a function.
+If we do not return a value with a function, then our function is returning _None_ by default. To return a value with a function we use the keyword _return_ followed by the variable we are returning. We can return any kind of data types from a function.
 
-- Returning string:
-  **Example:**
+- Returning a string:
+**Example:**
 
 ```py
-  def print_name(firstname):
-        return firstname
-  print_name('Asabeneh') # Asabeneh
+def print_name(firstname):
+    return firstname
+print_name('Asabeneh') # Asabeneh
 
-  def print_full_name(firstname, lastname):
-        space = ' '
-        full_name = firstname  + space + lastname
-        return full_name
-  print_full_name(firstname='Asabeneh', lastname='Yetayeh')
+def print_full_name(firstname, lastname):
+    space = ' '
+    full_name = firstname  + space + lastname
+    return full_name
+print_full_name(firstname='Asabeneh', lastname='Yetayeh')
 ```
 
-- Returning Number:
+- Returning a number:
 
 **Example:**
 
 ```py
-  def add_two_numbers (num1, num2):
-          total = num1 + num2
-          return total
-  print(add_two_numbers(2, 3))
+def add_two_numbers (num1, num2):
+    total = num1 + num2
+    return total
+print(add_two_numbers(2, 3))
 
-  def calculate_age (current_year, birth_year):
-      age = current_year - birth_year
-      return age;
-  print('Age: ', calculate_age(2019, 1819))
+def calculate_age (current_year, birth_year):
+    age = current_year - birth_year
+    return age;
+print('Age: ', calculate_age(2019, 1819))
 ```
 
-- Returning Boolean:
+- Returning a boolean:
   **Example:**
 
 ```py
-  def is_even (n):
-      if n % 2 == 0:
-          print('even')
-          return True
-      return False
-  print(is_even(10)) # True
-  print(is_even(7)) # False
+def is_even (n):
+    if n % 2 == 0:
+        print('even')
+        return True    # return stops further execution of the function, similar to break 
+    return False
+print(is_even(10)) # True
+print(is_even(7)) # False
 ```
 
-- Returning List:
+- Returning a list:
   **Example:**
 
 ```py
-  def find_even_numbers(n):
-      evens = []
-      for i in range(n+1):
-          if i % 2 == 0:
-              evens.append(i)
-      return evens
-  print(find_even_numbers(10))
+def find_even_numbers(n):
+    evens = []
+    for i in range(n+1):
+        if i % 2 == 0:
+            evens.append(i)
+    return evens
+print(find_even_numbers(10))
 ```
 
-### Function with default parameters
+### Function with Default Parameters
 
-Sometimes we pass default values to parameters, when we invoke the function if we do not pass an argument the default value will be used.
+Sometimes we pass default values to parameters, when we invoke the function. If we do not pass arguments when calling the function, their default values will be used.
 
 ```py
-  # syntax
-  # Declaring a function
-  def function_name(param = value):
+# syntax
+# Declaring a function
+def function_name(param = value):
     codes
     codes
-  # Calling function
-  function_name()
-  function_name(arg)
+# Calling function
+function_name()
+function_name(arg)
 ```
 
 **Example:**
 
 ```py
-  def greetings (name = 'Peter'):
+def greetings (name = 'Peter'):
     message = name + ', welcome to Python for Everyone!'
     return message
-  print(greetings())
-  print(greetings('Asabeneh'))
+print(greetings())
+print(greetings('Asabeneh'))
 
-  def generate_full_name (first_name = 'Asabeneh', last_name = 'Yetayeh'):
-      space = ' '
-      full_name = first_name + space + last_name
-      return full_name
+def generate_full_name (first_name = 'Asabeneh', last_name = 'Yetayeh'):
+    space = ' '
+    full_name = first_name + space + last_name
+    return full_name
 
-  print(generate_full_name())
-  print(generate_full_name('David','Smith'))
+print(generate_full_name())
+print(generate_full_name('David','Smith'))
 
-  def calculate_age (birth_year,current_year = 2019):
-      age = current_year - birth_year
-      return age;
-  print('Age: ', calculate_age(1819))
+def calculate_age (birth_year,current_year = 2019):
+    age = current_year - birth_year
+    return age;
+print('Age: ', calculate_age(1819))
 
-  def weight_of_object (mass, gravity = 9.81):
-      weight = str(mass * gravity)+ ' N' # the value has to be changed to string first
-      return weight
-  print('Weight of an object in Newton: ', weight_of_object(100)) # 9.81 gravity at the surface of Earth
-  print('Weight of an object in Newton: ', weight_of_object(100, 1.62)) # gravity at surface of Moon
+def weight_of_object (mass, gravity = 9.81):
+    weight = str(mass * gravity)+ ' N' # the value has to be changed to string first
+    return weight
+print('Weight of an object in Newtons: ', weight_of_object(100)) # 9.81 - average gravity on Earth's surface
+print('Weight of an object in Newtons: ', weight_of_object(100, 1.62)) # gravity on the surface of the Moon
 ```
 
-### Arbitrary number of arguments
+### Arbitrary Number of Arguments
 
-If we do not know the number of arguments we pass to our function we can create a function which can take arbitrary number of arguments by add \* before the parameter name.
+If we do not know the number of arguments we pass to our function, we can create a function which can take arbitrary number of arguments by adding \* before the parameter name.
 
 ```py
-  # syntax
-  # Declaring a function
-  def function_name(*args):
+# syntax
+# Declaring a function
+def function_name(*args):
     codes
     codes
-  # Calling function
-  function_name(param1, param2, param3,..)
+# Calling function
+function_name(param1, param2, param3,..)
 ```
 
 **Example:**
 
 ```py
-  def sum_all_nums(*nums):
-      total = 0
-      for num in nums:
-          total += num
-      return total
-  print(sum_all_nums(2, 3, 5))
+def sum_all_nums(*nums):
+    total = 0
+    for num in nums:
+        total += num     # same as total = total + num 
+    return total
+print(sum_all_nums(2, 3, 5))
 ```
 
-### Default and arbitrary number of parameters in function
+### Default and Arbitrary Number of Parameters in Functions
 
 ```py
 def generate_groups (team,*args):
@@ -357,58 +358,56 @@ def generate_groups (team,*args):
 generate_groups('Team-1','Asabeneh','Brook','David','Eyob')
 ```
 
-### Function as parameter of other function
+### Function as a Parameter of Another Function
 
 ```py
-  #You can pass functions around as parameters
-  def square_number (n):
-      return n * n
-  def do_something(f, x):
-      return f(x)
-  print(do_something(square_number, 3))
+#You can pass functions around as parameters
+def square_number (n):
+    return n * n
+def do_something(f, x):
+    return f(x)
+print(do_something(square_number, 3))
 ```
 
 ## 💻 Exercises: Day 11
 
-1. Declare a function _add_two_numbers_ and it takes two two parameters and it returns sum.
-2. Area of a circle is calculated as follows: area = π x r x r. Write a function which calculates _area_of_circle_.
-3. Write a function called add_all_nums which take arbitrary number of arguments and sum all the arguments. Check if all the list items are number types. If not give return reasonable feedback.
-4. Temperature in oC can be converted to oF using this formula: oF = (oC x 9/5) + 32. Write a function which converts oC to oF, _convert_celcius_to-fahrenheit_.
-5. Write a function called check-season, it takes a month parameter and returns the season:Autumn, Winter, Spring or Summer.
-6. Write a function called calculate_slope which return the slop of a linear equation
-7. Quadratic equation is calculated as follows: ax2 + bx + c = 0. Write a function which calculates solution set of a quadratic equation, _solve_quadratic_eqn_.
-8. Declare a function name print_list. It takes list as a parameter and it prints out each element of the list.
-9. Declare a function name reverse_list. It takes array as a parameter and it returns the reverse of the array (dont’ use method).
+1. Declare a function _add_two_numbers_. It takes two parameters and it returns a sum.
+2. Area of a circle is calculated as follows: area = π x r x r. Write a function that calculates _area_of_circle_.
+3. Write a function called add_all_nums which takes arbitrary number of arguments and sums all the arguments. Check if all the list items are number types. If not do give a reasonable feedback.
+4. Temperature in °C can be converted to °F using this formula: °F = (°C x 9/5) + 32. Write a function which converts °C to °F, _convert_celcius_to-fahrenheit_.
+5. Write a function called check-season, it takes a month parameter and returns the season: Autumn, Winter, Spring or Summer.
+6. Write a function called calculate_slope which return the slope of a linear equation
+7. Quadratic equation is calculated as follows: ax² + bx + c = 0. Write a function which calculates solution set of a quadratic equation, _solve_quadratic_eqn_.
+8. Declare a function named print_list. It takes a list as a parameter and it prints out each element of the list.
+9. Declare a function named reverse_list. It takes an array as a parameter and it returns the reverse of the array (use loops).
 
 ```py
-    print(reverse_list([1, 2, 3, 4, 5]))
-    # [5, 4, 3, 2, 1]
-    print(reverse_list1.(["A", "B", "C"]))
-    # ["C", "B", "A"]
+print(reverse_list([1, 2, 3, 4, 5]))
+# [5, 4, 3, 2, 1]
+print(reverse_list1(["A", "B", "C"]))
+# ["C", "B", "A"]
 ```
 
-10. Declare a function name capitalize_list_items. It takes list as a parameter and it returns the capitalized list of the items
-11.
-
-- Declare a function name add_item. It takes a list and an item parameter and it returns a list after adding the item
+10. Declare a function named capitalize_list_items. It takes a list as a parameter and it returns a capitalized list of items
+11. Declare a function named add_item. It takes a list and an item parameters. It returns a list with the item added at the end.
 
 ```py
-  food_staff = ['Potato', 'Tomato', 'Mango', 'Milk'];
-  print(  add_item(food_staff, 'Meat'))     # ['Potato', 'Tomato', 'Mango', 'Milk','Meat'];
-  numbers = [2, 3,7,9];
-  print(add_item(numbers, 5))      [2, 3,7,9,5]
+food_staff = ['Potato', 'Tomato', 'Mango', 'Milk'];
+print(  add_item(food_staff, 'Meat'))     # ['Potato', 'Tomato', 'Mango', 'Milk','Meat'];
+numbers = [2, 3, 7, 9];
+print(add_item(numbers, 5))      [2, 3, 7, 9, 5]
 ```
 
-- Declare a function name remove_item. It takes a list and an item parameter and it returns a list after removing an item.
+12. Declare a function named remove_item. It takes a list and an item parameters. It returns a list with the item removed from it.
 
 ```py
-  food_staff = ['Potato', 'Tomato', 'Mango', 'Milk'];
-  print(remove_item(food_staff, 'Mango'))  # ['Potato', 'Tomato', 'Milk'];
-  numbers = [2, 3,7, 9];
-  print(remove_item(numbers, 3))  # [2, 7, 9]
+food_staff = ['Potato', 'Tomato', 'Mango', 'Milk'];
+print(remove_item(food_staff, 'Mango'))  # ['Potato', 'Tomato', 'Milk'];
+numbers = [2, 3, 7, 9];
+print(remove_item(numbers, 3))  # [2, 7, 9]
 ```
 
-1.  Declare a function name sum_of_numbers. It takes a number parameter and it adds all the numbers in that range.
+13.  Declare a function named sum_of_numbers. It takes a number parameter and it adds all the numbers in that range.
 
 ```py
 print(sum_of_numbers(5))  # 15
@@ -418,9 +417,9 @@ print(sum_all_numbers(100)) # 5050
 
 ```
 
-2.  Declare a function name sum_of_odds. It takes a number parameter and it adds all the odd numbers in that range.
-3.  Declare a function name sum_of_even. It takes a number parameter and it adds all the even numbers in that - range.
-    Declare a function name evens_and_odds . It takes a positive integer as parameter and it counts number of evens and odds in the number.
+14.  Declare a function named sum_of_odds. It takes a number parameter and it adds all the odd numbers in that range.
+15.  Declare a function named sum_of_even. It takes a number parameter and it adds all the even numbers in that - range.
+16.  Declare a function named evens_and_odds . It takes a positive integer as parameter and it counts number of evens and odds in the number.
 
 ```py
     print(evens_and_odds(100))
@@ -428,17 +427,17 @@ print(sum_all_numbers(100)) # 5050
     # The number of evens are 51.
 ```
 
-15. Call your function factorial, it takes a whole number as a parameter and it return a factorial of the number
-    Call your function _is_empty_, it takes a parameter and it checks if it is empty or not
-16. Write different functions which take lists and it calculate_mean, calculate_median, calculate_mode, calculate_range, calculate_variance, calculate_std.
-17. Write a function called is_prime, which checks if a number is prime number.
-18. Write a functions which checks if all items are unique in the list.
-19. Write a function which checks if all the items of the list are the same data type.
-20. Write a function which check if variable if valid python variable
-21. Go the data folder and access the countries-data.py file.
+17. Call your function factorial, it takes a whole number as a parameter and it return a factorial of the number
+18. Call your function _is_empty_, it takes a parameter and it checks if it is empty or not
+19. Write different functions which take lists. They should calculate_mean, calculate_median, calculate_mode, calculate_range, calculate_variance, calculate_std (standard deviation).
+20. Write a function called is_prime, which checks if a number is prime.
+21. Write a functions which checks if all items are unique in the list.
+22. Write a function which checks if all the items of the list are of the same data type.
+23. Write a function which check if provided variable is a valid python variable
+24. Go to the data folder and access the countries-data.py file.
 
-- Create a function called the most_spoken_languages the world and it returns the 10 or 20 most spoken countries in the world in descending order
-- Create a function called the most_populated_countries and it return 10 or 20 most populated countries in descending order.
+- Create a function called the most_spoken_languages in the world. It should return 10 or 20 most spoken languages in the world in descending order
+- Create a function called the most_populated_countries. It should return 10 or 20 most populated countries in descending order.
 
 🎉 CONGRATULATIONS ! 🎉