Divide 2358 by 9 in your head

Question

Solve in your head, no long division. What is 2358 \div 9? Aim: under 15 seconds.

Accepted Answer

Digit sum: 2+3+5+8 = 18, divisible by 9, so the answer is a whole number. Fast route, anchor on an easy multiple of 9: 9 	imes 260 = 2340, \qquad 2358 - 2340 = 18 = 9 	imes 2, so 2358 \div 9 = 260 + 2 = 262. Alternative: \div 9 = \div 3 \div 3. 2358 / 3 = 786, and 786 / 3 = 262. Takeaway. Two tools stack here: the digit-sum test (tells you whether the answer is clean before you start) and anchoring on a nearby round multiple. Dividing by a near-round quotient guess and patching the remainder is almost always faster than digit-by-digit division.

Divide 2358 by 9 in your head

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