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, 237x5=2370/2=1185
Same way  you can also multiply by 50 

Multiplication by 4
Replace either with a repeated operation by 2.For example 124x4=248·2=4

Multiplication by 25
Multiply first by 100 and then divide by 4 For example37x25=3700/4=1850/2=925.

Multiplication by 8
Replace either with a repeated operation by 2. For example 124x8=248x4=496x2=992.

Multiplication by 45
Multiply first by 90and then divide by 2.For example37x45=37x90/2=3330/2=1665
Or see this method also  37 x45 = 37 (100/2  -10/2)= 3700/2-370/2=1850-185=1665

Multiplication by 55
Multiply first by 110and then divide by 2. For example37x55=37x110/2=4070/2=2035

Multiplication by 75
Multiply first by 300 and then divide by 4 .For example37x75=37x300/4=11100/4=2775

Multiplication by 125
Multiply first by 500 and then divide by 4 For example37x125=37x500/4=18500/4=4625

Multiplication by 150
Multiply first by 300 and then divide by 2 For example37x150=37x300/4=11100/2=5550

Multiplication by 175
Multiply first by 700 and then divide by 4 For example37x175=37x700/4=25900/4=6475

Multiplication by 225
Multiply first by 900 and then divide by 4 For example37x225=37x900/4=33300/4=8325

Multiplication by 275
Multiply first by 1100 and then divide by 4 
For example37x275=37x1100/4=40700/4=10175

A  Great   Time Saver 
Q A music shop has a sound system marked at Rs. 14000 on which a sales tax of  12.5% is chargeable. Find the total value a customer would have to pay for the sound system.
     sales tax  =  14000x12.5    =    14000x125    =  14x 500  =  7000   =1750
                                100                        1000                4                4
                          Rs 14000+1750 =Rs15750   Answer

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