Grade 3 · Unit 1: Number and place value

Inverse operations

Undo to check or find the unknown.

Undo it!

Opening a lock undoes closing it. In maths, inverse operations undo each other. Adding 25 is undone by taking away 25.

Addition and subtraction

A part-whole model shows both. Parts add to make the whole. Whole minus one part gives the other part.

Multiplication and division

Multiplication and division are inverses too. 4 × 7 = 28. So 28 ÷ 4 = 7.

Find the unknown

A number went into the machine and 91 came out. The machine adds 36. Work backwards: 91 − 36 = 55. ☐ = 55.

Words for each part

Numbers we add are addends; the answer is the sum. In 13 − 5 = 8, 5 is the subtrahend and 8 is the difference. In 24 ÷ 6 = 4, 24 is the dividend, 6 the divisor and 4 the quotient.

What I learnt

• I know which operations are inverses.
• I can use inverses to check and find unknowns.