You are already familiar with real numbers like

etc and operations of addition (+), subtraction (–), multiplication (×) and division (÷) on these numbers.

For example, 2 + 7 is a numerical expression formed from numbers 2 and 3 using the operation addition. The following are few examples of numerical expressions formed from real numbers and operations on them

14 – 6
5 × 10
7(4 + 2)
10 – (2 × 6)
8 + 7 ÷ 6

Numerical expressions have numbers in them, and often operations but they don’t include any variables:

However, sometimes in mathematics, letters called variables are also used as symbols to represent numbers. Study the following statement: The sum of two whole numbers is 10. What are the numbers?

Solution

• y If the first whole number is 0, then the second must be 10 because

0 + 10 = 10

• y If the first whole number is 1, then the second must be 9 because

1 + 9 = 10

• y If the first whole number is 2, then the second must be 8 because

2 + 8 = 10

• y If the first whole number is 3, then the second must be 7 because

3 + 7 = 10

• y If the first whole number is 4, then the second must be 6 because

4 + 6 = 10

• If the first whole number is m and the second is n, then m + n = 10

Note: In the above explanation, expressions like 0 + 10, 1 + 9, 2 + 8, 3 + 7 and 4 + 6 are called numerical expressions. But the expression m + n is called an expression of algebra or an algebraic expression.