These mental maths tips with examples show how to break a calculation into smaller steps. Use them to check a discount, add prices or tackle a number puzzle. You do not need to race: start with an answer you can explain, then build speed through practice.
I enjoy watching Lily solve the numbers on SBS’s Letters and Numbers. My own answers can take much longer. The methods below give me a few ways to approach a sum when the first solution does not come to mind.
1. Work out a discount using 10% and 5%
Suppose a fare costs $360 and has a 15% discount. First find 10% by dividing by ten: $36. Half of that gives 5%: $18. Add the two amounts to get a $54 discount. Finally, subtract $54 from $360. The new price is $306.
This method also helps with other discounts. For example, 20% is twice 10%, while 25% is a quarter of the price. Remember to subtract the discount when you want the amount left to pay.
2. Add the larger parts first
To calculate 58 + 26, split each number into tens and ones. Add 50 + 20 to make 70. Then add 8 + 6 to make 14. Put the parts together: 70 + 14 = 84.
Working from the larger parts gives you a rough answer early. That makes it easier to notice if your final answer is far too large or small.
3. Round a number, then adjust
For 593 + 680, add seven to 593 so it becomes 600. Now 600 + 680 = 1,280. You added seven that was not in the original question, so take it away: 1,280 − 7 = 1,273.
You can use the same idea for multiplication. Work out 89 × 6 as 90 × 6 − 6. That gives 540 − 6 = 534.
4. Mental maths tips with examples of multiplication
Break an unfamiliar table into facts you know. For 12 × 4, calculate 10 × 4 and 2 × 4. Add 40 + 8 to get 48.
To multiply by 15, multiply by ten and add half of that answer. For example, 24 × 15 = 240 + 120 = 360. To multiply by 16, add one more group of 24: 360 + 24 = 384.
Patterns help too. Multiplying a whole number by five gives an answer ending in zero or five. However, simply adding a zero works for multiplying whole numbers by ten, not for every decimal calculation.
5. Practise a few calculations and check them
Choose two or three sums you can work through without rushing. Say or write down your method, then check the result. If you make a mistake, look for the step that went wrong before trying another question.
For mixed calculations, the order matters. Our guide to BODMAS explains where brackets and multiplication fit. You can also use our times tables practice routine with your child.
Put these mental maths tips with examples into practice
Try a number challenge in Countdown Letters and Numbers, or explore Magic Hexagon for a different puzzle. The badges below open the store listings, where you can check the current features and purchase options.
