# How to solve an expression through substitution

• Substitution means putting numbers in place of letters to calculate the value of an expression.
• An expression can be a combination of numbers, letters and operators, grouped together.

Look at the examples below:

## Example

If $$a~=~2$$ and $$b~=~5$$

Find $$3a~+~2b$$

How to solve the expression:

$$3a~+~2b$$

Substitute $$a$$ with the value $$2$$ and $$b$$ with $$5$$

${3}\times{2}~+~{2}\times{5}$

$=~6~+~10$

$=~16$