A and B can complete a work in 24 days and 36 days respectively. If they work together for 8 days, how much work is left?

Answer: B. 1/3
In 8 days, A and B together complete 8*(1/24 + 1/36) = 8*(5/72) = 40/72 = 5/9 of the work. Therefore, 1 - 5/9 = 4/9 of the work is left.
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