# Evaluate Solutions when there are Two Unknowns in an Expression

In this worksheet, students will evaluate an expression by substituting in the values of two unknowns.

Key stage:  KS 2

Curriculum topic:   Algebra

Curriculum subtopic:   Use Algebra Formulae

Difficulty level:

#### Worksheet Overview

In this activity, we will substitute values of unknowns to evaluate an expression.

To substitute just means to swap something

Like with football - one player comes off the pitch and one comes on in their place!

They are swapped!

Let's have a look at an example.

Example

When a = 5 and b = 10

What is the value of 2a + 4b?

2a + 4b = (2 x a) + (4 x b)
When a = 5 and b = 10 we substitute them
(2 x 5) + (4 x 10)
= 10 + 40
= 50

Let's try some of these - be very careful with any negatives!

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