Jul31

Mental Math: Multiplying by 25 and 75

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multiplying by 25

In this post we are going to learn a simple way of multiplying by 25 and 75. First, we’ll learn the method and then we’ll give mental math a shot.

Multiplying by 25:

The number 25 is 100 divided by 4. So, in order to multiply by 25 what we have to do is multiply by 100 and then, divide by 4. Another trick to divide by 4 is to first divide by 2, then divide by 2 again.

For example: 17 x 25

First we multiply the number by 100:

17 x 100 = 1700

Now, we divide by 4, which would be the same thing as dividing twice by 2:

1700 / 2 = 850

850 / 2 = 425

By following this method, we’ll end up with 17 x 25 = 425

Mental math exercise: try out this method with 32 x 25 = 800

Multiplying by 75:

75 = 3 (100 / 4), so, in order to multiply by 75, you need to multiply by 3, then multiply by 100 and lastly, divide by 4. To divide by 4, we use the same method as before: divide two times by 2.

For example: 13 x 75

First, we multiply the number by 3:

13 x 3 = 39

Now, we multiply by 100:

39 x 100 = 3900

The last step is to divide by 4, and in order to do so we just divide twice by 2:

3900 / 2 = 1950

1950 / 2 = 975

We end up with, 13 x 75 = 975

Mental math exercise: try out this method with 16 x 75 = 1200

If you want to practice mental math, multiplying by 25 and 75, go to Smartick and try it for free!

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