Have you ever seen people performing lightning fast math calculations and wondered how they did it? I remember watching Scott Flansburg, dubbed “The Human Calculator” and famed for his fast mental calculations, doing these instant calculations in his head. I was intrigued and began to learn some of these math tricks over the years.
I’ll teach you an easy multiplication trick that you can learn in less than 3 minutes. You will be multiplying 2-digit numbers in your head with ease in no time.
This method works for numbers that are slightly smaller than 100, typically between 90 and 99. I’ll be using the numbers 93 and 98 to explain how this works.
Step 1: Subtract Both Numbers from 100
First, subtract 93 and 98 from 100 to get 7 and 2 respectively.
Write the differences next to the numbers (shown in red below).
Step 2: Subtract the Difference from the Number
Subtract one of the results obtained in Step 1 from the number that is diagonally opposite. For instance, subtract 2 from 93 (shown below) or 7 from 98. Either way, the result will be 91.
Step 3: Multiply the Differences
Multiply the results obtained in Step 1.
7 x 2 = 14.
[Tip: If you get a number with one digit, prepend it with a 0(zero)]
Combine the results from Step 2 and 3 - 91 and 14 - to get the final answer of 9114.
Time for Some Practice
Try the following questions on paper and see how fast you can work out the answers. you should take less than 15 seconds for each question.
- 91 x 95
- 97 x 92
- 94 x 93
- 99 x 95
- 96 x 94
- 95 x 97
Once you are get good at this, work out the answers in your head
A Quick Lesson on Multiplying Numbers Greater than 100
You can use a variation of this technique to multiply numbers slightly greater than 100, say 104 and 107.
- First, subtract 100 from 104 and 107 to get 4 and 7 respectively.
- Next, add to the number that is diagonally opposite to get 111 (104+7 or 107+4).
- Finally, multiply the differences to get 28 (7x4=28). Combine the results, 111 and 28 to get the final answer of 11,128.
Now, try the following questions
- 103 x 109
- 101 x 106
- 105 x 107
- 106 x 106
- 107 x 102
- 101 x 108