Here are 5 Mental Math Tricks I taught my Kids!

When my eldest daughter, Rita, first learnt how to add and subtract numbers, she was so excited about it that she asked me to give her problems when she came back home. She would keep working on problems day and night and would come up with problems of her own too. Once she was done with the set that I had given her, she would come scuttling back to have me check her answers. Her face would light up each time I told her that she got them all right.

A girl working on a math problem on the whiteboard.
Learning math is fun!

The madness for mathematics that started way back then went on and today, she is a math genius who can do complex math problems all in her head. My sons, Eric and Aaron, too, can do quick calculations mentally.

I had learnt quite a few mental math tricks as a kid, most of which I’ve shared with my kids. Here are a few:

Easy mental math tricks for kids

Mental math can not only help kids do calculations mentally but also improve reasoning abilities and problem-solving skills.

Trick 1: Multiplying a number by 5

To multiply a number by 5, simply divide the number by 2 and multiply it by 10.

For example, multiply 86 by 5.

Step 1: Divide 86 by 2 = 43

Step 2: Multiply 43 by 10 = 430

Answer: 430

This is one of the first and easiest tricks I’ve taught my kids. Once your kids get the hang of it, they’ll take only a moment to find the answer.

Trick 2: Multiplying a double-digit number by  11

Multiplying any double-digit number by 11 takes only a moment. All you have to do is add up the two numbers and place the sum in between the two numbers.

For example, multiply 54 by 11

Step 1: Add 5 and 4 = 9

Step 2: Place 9 in between 5 and 4 = 594

Answer: 594

Trick 3: Multiplying a number by 6

This trick is only helpful when multiplying even numbers by 6. You will have to divide the number by 2 to get the first digit of the answer. The next digit will be the number you divided 6 with.

For example, multiply 8 by 6

Step 1: Divide 8 by 2 = 4

Step 2: Place 8 after 4 = 48

Answer: 48

Trick 4: Multiplying a number by 9

Once my kids mastered the simple tricks such as those mentioned above, I taught them tricks like this one.

To quickly multiply a number by 9, you should subtract 1 from the number to get the first digit of the answer. Then, subtract this number from 10 to get the second digit of the answer.

For example, multiply 7 by 9

Step 1: Subtract 1 from 7 = 6

Step 2: Subtract 7 from 10 = 3

Step 3: Place the two together = 63

Answer: 63

Trick 5: Squaring a double-digit number ending with 5

Once your kids learn how to square numbers, you could teach them this trick to square numbers ending with 5. What you have to do is add 1 to the first digit of the number (being squared) and multiply the sum to the first digit of the original number (being squared). Your answer will be this answer followed by 25.

For example, square 45

Step 1: Add 1 to 4 = 5

Step 2: Multiply 5 by 4 = 20

Step 3: Place 25 after 20: 2025

Answer: 2025

These are just 5 of the mental math tricks I can think of at the spur of the moment. Do you know any other mental math tricks? Share them in the comments section.


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