Mental Math Challenge: 10 Quick Sums to Solve in Your Head

This mental math challenge gives you ten quick calculations to solve in your head, with handy tricks for multiplying by 11, 25 and 99, finding percentages, squaring numbers and adding in smart pairs, plus a look at the human computer Shakuntala Devi and the Japanese soroban abacus. Try each sum without a calculator.

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🎯 Daily Trivia Challenge • 🧠 10 Questions • ⏱️ 90 Seconds

Question 1 / 10 Time: 90s

Multiplying
What is 25 times 16?
Percentages
What is 15 percent of 80?
Multiplying
What is 99 times 7?
Subtracting
What is 1,000 minus 387?
Dividing
What is 48 divided by one half?
Squares
What is 13 squared, or 13 times 13?
Multiplying
What is 125 times 8?
Fractions
What is half of three quarters?
Adding
What is 37 plus 48 plus 63?
Tricks
What is 11 times 34?

Explanations: answer key for all 10 questions

Q1: What is 25 times 16?
Answer: 400
Think of 25 times 4 as 100. Since 16 is 4 times 4, the answer is 100 times 4, which is 400.
Q2: What is 15 percent of 80?
Answer: 12
10 percent of 80 is 8, and 5 percent is half of that, 4. Adding them gives 12.
Q3: What is 99 times 7?
Answer: 693
Work out 100 times 7, which is 700, then take away one 7. That gives 693.
Q4: What is 1,000 minus 387?
Answer: 613
Count up from 387: 13 gets you to 400, and 600 more gets you to 1,000. Together that makes 613.
Q5: What is 48 divided by one half?
Answer: 96
Dividing by one half is the same as multiplying by 2. Many people answer 24 by mistake, confusing it with dividing by 2.
Q6: What is 13 squared, or 13 times 13?
Answer: 169
13 times 10 is 130 and 13 times 3 is 39. Adding them gives 169.
Q7: What is 125 times 8?
Answer: 1,000
125 is one eighth of 1,000, so multiplying it by 8 gives exactly 1,000. Knowing number pairs like this saves time.
Q8: What is half of three quarters?
Answer: Three eighths
Halving a fraction doubles the bottom number. So half of 3/4 is 3/8. The top number stays the same.
Q9: What is 37 plus 48 plus 63?
Answer: 148
Pair 37 with 63 first to make 100, then add 48. Grouping numbers that make round totals is a quick mental math trick.
Q10: What is 11 times 34?
Answer: 374
To multiply a two-digit number by 11, add its digits and put the sum in the middle: 3 plus 4 is 7, so the answer is 374.

Mental Math Challenge – Calculating Without a Calculator

Mental math is the skill of working out calculations in your head. It is useful when shopping, splitting a bill, estimating time or checking whether a calculator answer looks right. People who are good at mental math are not always faster at arithmetic; they usually know clever shortcuts that turn hard sums into easy ones.

Many shortcuts rely on round numbers. Multiplying by 99 is easier as multiplying by 100 and subtracting once. Adding 37, 48 and 63 is quicker if you pair 37 with 63 to make 100. Multiplying by 25 is easier when you remember that four 25s make 100. Percentages become simple when you find 10 percent first and build from there.

Some tricks look like magic. To multiply a two-digit number by 11, add its two digits and place the sum between them, carrying if the sum is 10 or more. To square a number ending in 5, multiply the first digit by the next number and add 25 to the end, so 35 squared is 3 times 4, or 12, followed by 25, giving 1,225.

Shakuntala Devi, an Indian mental calculator known as the human computer, amazed audiences around the world. In 1980, she multiplied two 13-digit numbers in her head in seconds, a feat recorded by Guinness World Records.

In Japan, many children learn the soroban, a type of abacus. With practice, they imagine the beads in their minds and calculate at astonishing speed.

Practicing a few sums every day sharpens your number sense, improves memory and makes everyday math far less stressful.

What This Quiz Teaches

This quiz is perfect for students, parents and anyone who wants faster math.

Shortcuts for multiplying by 11, 25 and 99
How to find percentages quickly
Counting up to subtract
Dividing by fractions without mistakes
Squaring numbers in your head
Shakuntala Devi and the soroban abacus

Quick Facts About Mental Math

The Mental Calculation World Cup is held every two years.
The Trachtenberg system is a famous method for fast mental arithmetic.
Estimating first helps you catch calculator mistakes.
Many people find adding easier from left to right.
Abacus training is popular in parts of Asia.
Short daily practice works better than long sessions.