The most useful mental maths habit is this: rewrite a hard calculation as an easier one before you start working it out. Most of the tricks students pick up, from multiplying by 11 to squaring numbers that end in 5, are this same idea in different clothes. Once you see the pattern, you stop memorising shortcuts and start building them yourself.
Speed matters less than accuracy here. A method you can check in your head is worth more in an exam than a clever shortcut you only half remember. The tricks below are ones we return to with students again and again, and each one comes with a quick way to confirm the answer.
Break numbers apart before you multiply
Splitting one number into friendlier parts is the workhorse of mental arithmetic. To work out 7 × 64, think of 64 as 60 + 4. Then 7 × 60 is 420, 7 × 4 is 28, and the total is 448. Students who try to hold the whole problem in one go tend to lose track halfway. Splitting keeps each step small enough to hold in your head.
The same idea works for multiplying by numbers near 100. For 47 × 98, treat 98 as 100 − 2. That gives 4,700 − 94, which is 4,606. Look for the number that is closest to a round figure, and use the round figure as your anchor.
Multiplication shortcuts worth memorising
Some patterns come up so often that they are worth knowing cold.
- Multiplying by 11: for a two-digit number, add its two digits and place the result in the middle. For 36 × 11, 3 + 6 = 9, so the answer is 396. If the digits add to more than 9, carry the one. For 87 × 11, 8 + 7 = 15, so you get 8 + 1 in front, 5 in the middle and 7 at the end: 957.
- Multiplying by 9: multiply by 10 and subtract the number once. For 9 × 7, that is 70 − 7 = 63.
- Squaring a number ending in 5: take the tens digit, multiply it by the next whole number up, then write 25 at the end. For 35², 3 × 4 = 12, so the answer is 1,225.
- Difference of two squares: numbers that sit equally either side of a round figure multiply neatly. For 53 × 47, that is (50 + 3)(50 − 3) = 2,500 − 9 = 2,491.
Do not try to learn all of these at once. Pick two or three that suit the numbers you meet most, practise them for a week, and add more when the first ones feel automatic.
Percentages and fractions without a calculator
Percentages are where many students lose marks through panic rather than difficulty. Find 10% first, because it is just a shift of the decimal point. Then build from there. For 15% of 80, 10% is 8 and 5% is half of that, which is 4. Add them to get 12.
Fractions follow the same logic. You will often recognise that 1/4 is 0.25, 3/4 is 0.75 and 1/8 is 0.125 without working anything out. Spending a few minutes learning these common equivalents saves real time in timed papers.
Subtract by counting up, not by borrowing
Long subtraction with borrowing is error-prone when done in your head. Try the complement method instead. To work out 1,000 − 387, ask how far 387 is from 1,000. Add 13 to reach 400, then 600 more to reach 1,000. The gap is 613. Counting up in friendly chunks is often faster and easier to check than borrowing across several columns.
Check your answer before you move on
A quick estimate is the best safety net you can have. If 49 × 21 comes out as 10,290, round the numbers to 50 × 20 and you expect something close to 1,000. The answer is clearly wrong, and you can catch it in seconds. Students who estimate first make fewer careless mistakes in exams, because they notice when something looks off.
Practising mental maths well enough to use it under pressure
Mental maths improves through short, regular practice rather than occasional marathons. Five minutes a day with a few problems from the same pattern will do more than an hour once a fortnight. Say your working aloud or write the steps briefly at first, so you can see where your thinking goes wrong. Over time, the steps shrink until they become instinct.
This is also where a good teacher earns their keep. At our centre, small batches of four to eight students mean every learner gets to explain their method, and our teachers can see quickly whether a student is using a shortcut correctly or simply guessing. Our teachers align practice with the way each board assesses working, so students learn methods that earn method marks. Students following our CBSE tuition or ICSE and ISC tuition get this practice built into weekly worksheets and monthly mock papers.
Frequently Asked Questions
Are mental maths tricks useful for board exams, or only for speed?
They help with both, but accuracy comes first. Many board questions award method marks, so a student who can explain a clean decomposition or estimate a result earns credit even when a calculation slips. Shortcuts are most valuable when you can also check them, which is why we teach students to estimate before they write a final answer.
How long does it take to get comfortable with these methods?
Most students become confident with one or two methods within a few weeks of daily practice of about five minutes. The timeline depends on how often you practise and how many problems you attempt. We track progress against each student's plan, so families can see which methods are settling and which need more time.
Should I learn a trick if I do not understand why it works?
It is better to understand first. A trick you can explain is one you can rebuild when you forget it. Ask yourself why 11 works with digit sums, or why 9 × 7 becomes 70 − 7. When a method has a reason behind it, it stays with you under exam conditions.
How does INACADEMICS help a student who finds mental maths difficult?
We start with a short diagnostic to find where a student's number sense breaks down, then place them in a small batch with a subject specialist. Weekly worksheets reinforce one or two methods at a time, and monthly mocks show whether the methods hold up under timed conditions. Parents receive regular updates tracked against the plan.
Start with one trick this week
Pick one method from this article, practise it for five minutes a day, and check every answer with an estimate. Within a fortnight you should notice that calculations feel less like hard work. If you would like a clearer picture of where you stand, book free counselling with our team, call or WhatsApp us on +91 9014010410, or drop into our centre in Kokapet. For more practical study guides, visit our blog.