How_To_Be_Good_At_Math

CALCULATING • SHOPKEEPER’S ADDITION 93

Shopkeeper’s addition

People who work in shops often need to work out quickly how much

change to give a customer. They often count up in their heads to

help them work out the correct change. This method of subtracting

is called shopkeeper’s addition.

First, let’s add 5p to get £7.40.

Peter’s groceries cost £7.35,

and he pays with a £10 note.

How much change is he due?

We can write this as £10.00 − £7.35

Next, we add 60p to take

us to £8.

Now, we can add £2 to

take us up to £10.

Finally, we combine the amounts

we’ve added to find the total

difference:

£0.05 + £0.60 + £2.00 = £2.65

So, Peter is due £2.65 change

from his £10 note.

Be the shopkeeper

Can you use the method we’ve

learned to work out the change for

these bags of shopping?

TRY IT OUT

Answers on page 319

Cost £3.24

Paid for with

a £10 note.

Cost £17.12

Paid for with

a £20 note.

Cost £59.98

Paid for with

two £50 notes.

£7.35 + £0.05 = £7.40

£7.40 + £0.60 = £8.00

£8.00 + £2.00 = £10.00

£7.35 + £2.65 = £10.00

£10.00 − £7.35 =?

£10.00 − £7.35 = £2.65

092_093_Subtracting_with_a_number_line_Shopkeepers_addition.indd 93 29/02/2016 14:10