Easy Maths Tricks
Master these simple tricks and improve your mental calculation speed.
✋ Multiply by 5
Divide the number by 2 and multiply the result by 10.
48 × 5
= 24 × 10
= 240
⚡ Multiply by 11
For a two-digit number, add the two digits and place the result between them.
Put 5 between 2 and 3
23 × 11 = 253
🎯 Square Numbers Ending in 5
Multiply the first digit by the next number and add 25.
Add 25 → 1225
Therefore, 35² = 1225
➗ Multiply by 9
Multiply by 10 and subtract the original number.
= 470 − 47
= 423
💯 Percentage Trick
To find 10%, simply move the decimal point one place to the left.
20% = ₹170
5% = ₹42.50
15% = ₹127.50
🚀 Square Near 100
Use the formula (100 − x)².
98² = 9604
🔢 Divisibility by 9
Add all the digits. If the total is divisible by 9, the original number is also divisible by 9.
Therefore,
729 is divisible by 9.
🏆 Multiplication Near 100
Use the difference from 100 to calculate quickly.
96 → −4
97 − 4 = 93
3 × 4 = 12
Answer = 9312
🔟 Multiply by 10, 100 & 1000
Simply add zeros when working with whole numbers.
×100 → 2 zeros
×1000 → 3 zeros
25 × 100 = 2500
25 × 1000 = 25000
➖ Subtraction from 1000
Subtract each digit from 9, except the last digit from 10.
= 626
🔄 Doubling & Halving
Double one number and halve the other to keep the same product.
= 8 × 50
= 400
➕ Sum of 1 to N
The sum of 1+2+3+...+N = N(N+1)/2.
= 100 × 101 ÷ 2
= 5050
💡 Find 12.5%
Divide by 8 (half of 25%).
= 560 ÷ 8
= 70
🔢 Divisibility by 11
Alternately add and subtract digits. If result is 0 or divisible by 11, the number is too.
Not divisible by 11
91808 ÷ 11 = 834.36...
🔁 Sum of Consecutive Odds
The sum of the first N odd numbers = N².
= 5² = 25
🧩 Cast Out Nines
To check addition, cross out digits that add to 9. If remainders match, the sum is likely correct.
234 → 2+3+4=9→0
567 → 5+6+7=18→9→0
801 → 8+0+1=9→0
0 = 0 + 0 ✓
📐 Difference of Squares
a² − b² = (a+b)(a−b). Use this to multiply or simplify.
= 50² − 3²
= 2500 − 9 = 2491
⚖️ Average Trick
If two numbers are equidistant from a round number, their average is that round number.
Both are 3 from 50
Average = 50
🧠 Practice Time!
Try solving these without using a calculator.