improved readability, fixed some typos

09_Day_Higher_order_functions/09_day_higher_order_functions.md

@@ -557,7 +557,7 @@ console.log(users) // sorted ascending
 ### Exercises: Level 1
 
 ```js
-const countries = ['Finland', 'Sweden', 'Denmark', 'Norway', 'IceLand']
+const countries = ['Estonia', 'Finland', 'Sweden', 'Denmark', 'Norway', 'Iceland']
 const names = ['Asabeneh', 'Mathias', 'Elias', 'Brook']
 const numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
 const products = [
@@ -602,9 +602,9 @@ const products = [
 1. Find the total price of products by chaining two or more array iterators(eg. arr.map(callback).filter(callback).reduce(callback))
 1. Find the sum of price of products using only reduce reduce(callback)
 1. Declare a function called **_categorizeCountries_** which returns an array of countries which have some common pattern(you find the countries array in this repository as [countries.js](../09_Day_Higher_order_functions/09_day_starter/data/countries_data.js) (eg 'land', 'ia', 'island','stan')).
-1. Create a function which return an array of objects, which is the letter and the number of times the letter use to start with a name of a country.
+1. Create a function which return an array of objects, which is the letter and the number of times the letter is used to start with a name of a country.
 1. Declare a **_getFirstTenCountries_** function and return an array of ten countries. Use different functional programming to work on the countries.js array
-1. Declare a **_getLastTenCountries_** function which which returns the last ten countries in the countries array.
+1. Declare a **_getLastTenCountries_** function which returns the last ten countries in the countries array.
 1. Find out which _letter_ is used many _times_ as initial for a country name from the countries array (eg. Finland, Fiji, France etc)
 
 ### Exercises: Level 3