Six workers, ten days, one wall, now two walls in eight days

Question

Six identical workers build one wall in 10 days. Solve in your head. How many workers are needed to build two walls in 8 days? Aim: under 15 seconds.

Accepted Answer

Work in worker-days, the invariant unit: - One wall costs 6 	imes 10 = 60 worker-days. - Two walls cost 120 worker-days. - You have only 8 days, so the crew must supply 120 / 8 = 15 worker-days per day, meaning 15 	ext{ workers}. Takeaway. The same conserved-quantity move (worker-days) solves for whichever variable is unknown, here it is headcount, not time. Compute total work, divide by the time allowed, and read off the number of workers; no formula juggling required.

Six workers, ten days, one wall, now two walls in eight days

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