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!
Learn More:
- Two Ways of Dividing Fractions and Some Examples
- Strategy for Multiplying by 2, 4, and 8
- Multiplying Numbers Followed by Zeros
- Alternative Methods for Multiplication: Russian and Hindu Methods
- Multiplying and Dividing Decimal Numbers by Powers of 10
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