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Multiplication Tricks - Be a Human Calculator

By Edited Apr 22, 2015 1 2

Multiplication Tricks – Be a Human Calculator

In today's world, use of mathematics is necessary. Human brain is very complex. It has the power of remembering everything you see or you hear. Just imagine you are in a store and you want to buy an item. It says item is $25, but it is discounted 25%. Right away you say to yourself wish I knew how much it is and if have enough money to buy it. Sure you have the option to wait for the clerk and ask him or her or you can use some multiplication tricks to arrive at the answer.

Wouldn't it be nice if you had the answer before the checkout girl in the store rings up the item and gives you a change back? I will explain few of the tricks today in this article.

1. How to square a number that ends in 5

To square a number that ends in 5. The last two digit of the answer will always end in 25. Now, take the first digit in tens position and multiply (itself+1). This is the first part of the answer.

Example1: Square of 25

We know from above discussion last two digits are 25. Now, number in tens position is 2. Multiply 2 by (itself+1). In other words multiply 2 and 3 which is 6. This is the first part of the answer. So the answer is 625.

So, in out store problem above, now we know 25 times 25 is 625. Since discount is in percent, we need to divide 625 by 100 which is 6.25. In other words discount is $6.25

Example 2: Square of 85.

Last two digits are 25. Now, number in tens position is 8. Multiply 8 by (itself+1). In other words multiply 8 and 9 which is 72. This is the first part of the answer. So answer is 7225.

I will have more multiplication tricks in coming articles
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Comments

Jun 3, 2010 10:49am
eileen
Am I reading this right or should the first sum be 2x3 =6 not 2 and 2

Good easy way of working it out I will try to remember this. thumbs up
Jun 3, 2010 11:34am
carburized
Eileen: You are correct. It should be 2x3 not 2x2. I guess I should have paid more attention when writing. Thank you
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