Use complements to 10, 100, and 1000
One of the strongest mental maths habits is spotting complements. If a student sees 68 + 32, the answer is easier because 68 needs 32 to make 100. If they see 295 + 47, they can add 5 first to reach 300, then add the remaining 42 to get 342. This method works because the brain handles round numbers more easily.
Complements also help in subtraction. Instead of struggling with 1000 - 678 by borrowing across zeros, count up from 678 to 700, then to 1000. The difference is 22 + 300, which is 322. Students who practise this regularly become faster and more confident with money, measurement, and exam arithmetic.
Break multiplication into friendly parts
Multiplication becomes easier when numbers are split into parts. To solve 17 x 6, think 10 x 6 plus 7 x 6, giving 60 + 42 = 102. To solve 24 x 25, use 25 as one quarter of 100. Since 24 x 100 is 2400, one quarter is 600. The answer arrives quickly, but the student can still explain why it works.
This is better than memorising a trick that only works for one type of question. Breaking numbers apart works for many cases: 39 x 8 as 40 x 8 minus 8, 52 x 5 as half of 52 x 10, and 99 x 14 as 100 x 14 minus 14. The method is flexible, which is what students need in real tests.
Turn percentages into fractions
Percentages are easier when students know common equivalents. Ten percent is one tenth, twenty-five percent is one quarter, fifty percent is one half, and seventy-five percent is three quarters. So 25 percent of 360 is one quarter of 360, which is 90. This is faster than writing a long formula for every percentage question.
For less obvious percentages, combine friendly parts. Fifteen percent is ten percent plus five percent. If the amount is 800, ten percent is 80 and five percent is 40, so fifteen percent is 120. This method is useful for discounts, interest, profit and loss, and everyday shopping calculations.
Estimate before solving exactly
Estimation is not a replacement for exact answers; it is a safety check. Before solving 49 x 21, estimate 50 x 20, which is about 1000. If the exact answer you get is 1029, it is believable. If you get 10,029, the estimate warns you that a place-value error happened.
Students should learn to ask, 'Should the answer be small, medium, or large?' before calculating. This habit catches many careless errors in multiple-choice exams because some options are clearly outside the expected range. It also helps students choose between close-looking answers under time pressure.
Practise orally, then in writing
Mental maths improves through repeated short sessions. A parent or teacher can call out five questions each day and ask the learner to explain the thinking, not just the answer. Explanation matters because it reveals whether the student is using a reliable method or guessing quickly.
After oral practice, students should write a few examples to connect mental methods with formal school working. This prevents the common problem where a learner can answer fast in a game but cannot show working in class. The goal is speed with understanding, not speed instead of understanding.
Key Takeaways
- Mental maths improves when students understand the method behind the shortcut.
- Breaking numbers apart is safer than memorising disconnected tricks.
- Estimation helps students catch errors before submitting answers.