Substituting into an expression (1 step)

Introduced in the Year 6 curriculum as: "Use simple formulae"

Given an expression like:

? - 5

If we know what number ? represents, we can replace ? with that number and work out a value for the expression.


Example 1:

Work out ? - 5 if ? = 8

Well, replace ? with 8

? - 5 becomes 8 - 5 = 3

This is called 'substituting in'


Example 2:

Work out 4? if ? = 3

So, if ? = 3

4? = 12

Remember, 4? means 4 times ?


Example 3:

75 - y = 30 What is the value of y?

We know that 75 - 45 = 30.

So y = 45


Example 4:

4y + 20 = 300 What is the value of y?

We know that 280 + 20 = 300.

So 4y = 280

So y = 70


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