1.2.4 Multiplying by 75 Trick

In a similar fashion, you can multiply by 75 by treating it as ¾ × 100. So when you multiply by 75, first divide the number you’re multiplying by 4, then multiply by 3, then move the decimal over two places to the right.

Example: 76 × 75

Step	Calculation
Divide by 4	76 ÷ 4 = 19
Multiply by 3	19 × 3 = 57
Multiply by 100	57 × 100 = 5700

Example: 42 × 75

Step	Calculation
Divide by 4	42 ÷ 4 = 10.5
Multiply by 3	10.5 × 3 = 31.5
Multiply by 100	31.5 × 100 = 3150

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Dividing by 75

Again, you can use the same principle to divide by 75 as well, only you multiply by 4/3 then divide by 100 (or move the decimal place over two digits to the left).

Example: 81 ÷ 75

Step	Calculation
Multiply by 4	81 × 4 = 324
Divide by 3	324 ÷ 3 = 108
Divide by 100	108 ÷ 100 = 1.08

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Problem Set 1.2.4

* Questions marked with an asterisk accept answers within 5% tolerance.