Divide 1800 by 25 quickly

Question

Twenty-five divides awkwardly by hand but cleanly with a reframe. Solve in your head. What is 1800 \div 25? Aim: under 8 seconds.

Accepted Answer

Because 25 = 	frac{100}{4}, dividing by 25 means dividing by 100 and multiplying by 4: \frac{1800}{25} = \frac{1800}{100} 	imes 4 = 18 	imes 4 = 72. So 1800 \div 25 = \mathbf{72}. Strip two zeros to 18, then quadruple. Check: 25 	imes 72 = 1800. Correct. Takeaway. Divide by 25 = "\div 100, then 	imes 4." The reciprocal-of-100 shortcuts (25, 50, 125) turn division into a shift plus a tiny multiply.

Divide 1800 by 25 quickly

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