Mathematics Trick

1. Multiplication by 5
It's often more convenient instead of multiplying by 5 to multiply first by 10 and then divide by 2.
For example,
137·5 = 1370/2 = 685.

2. Division by 5
Similarly, it's often more convenient instead to multiply first by 2 and then divide by 10.
For example,
1375/5 = 2750/10 = 275.

3.Division/multiplication by 4
Replace either with a repeated operation by 2.
For example,
124/4 = 62/2 = 31. Also,
124·4 = 248·2 = 496.

4.Division/multiplication by 25
Use operations with 4 instead.
For example,
37·25 = 3700/4 = 1850/2 = 925.

5.Division/multiplication by 8
Replace either with a repeated operation by 2.
For example,
124·8 = 248·4 = 496·2 = 992.

6.Division/multiplication by 125
Use operations with 8 instead.
For example,
37·125 = 37000/8 = 18500/4 = 9250/2 = 4625.

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