Time and money problems

The idea

Money problems become much easier if you pick one unit and stick to it: either work in pounds with decimals (£2.40) or convert everything to pence (240p). Never mix the two in one calculation. When you add or subtract amounts, line up the decimal points so pounds stay under pounds and pence under pence.

For change, count up from the price to the amount paid, or subtract carefully — and check your change by adding it back to the price.

Time problems work like a number line. To add a duration, jump to the next whole hour first, then add what is left. Remember there are 60 minutes in an hour, so minutes never reach 60 when you write a clock time.

Worked example

Amara buys 3 notebooks at £2.40 each and a pen for £5.25. She pays with a £20 note. How much change does she get?

1. Cost of the notebooks: 3 × £2.40 = £7.20.
2. Total spent: £7.20 + £5.25 = £12.45.
3. Change: £20.00 − £12.45.
4. £20.00 − £12.45 = £7.55. Check: £12.45 + £7.55 = £20.00 ✓

Answer: £7.55

Watch out

• Writing £2.40 as 2.4 and then treating the 4 as 4 pence instead of 40 pence.
• Adding times as if there were 100 minutes in an hour (09:47 + 38 minutes is 10:25, not 09:85).
• Forgetting the second step — finding the total cost but not the change.