Divide 2900 by 25 without dividing

Question

Solve in your head, no long division. What is 2900 \div 25? Aim: under 5 seconds.

Accepted Answer

25 = 100/4, so dividing by 25 is multiplying by 4 and dividing by 100: \frac{2900}{25} = \frac{2900 	imes 4}{100} = \frac{11600}{100} = 116. Multiplying by 4 is just doubling twice: 2900 	o 5800 	o 11600. Takeaway. Treat 25, 50, and 125 as fractions of powers of ten: \div 25 = 	imes 4/100, \div 50 = 	imes 2/100, \div 125 = 	imes 8/1000. The same idea in reverse makes multiplication easy: 	imes 25 = 	imes 100 / 4, so 76 	imes 25 = 7600/4 = 1900.

Divide 2900 by 25 without dividing

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