B and C takes 5 times than A to complete a piece of work. If three together do that work in 15 days, then in how many days A, alone will do that work./B तथा C किसी काम को करने में A का 5 गुना समय लेता है, यदि तीनों मिलकर उस काम को 15 दिनों में समाप्त करते हैं, तो A अकेला उसी काम को कितने दिनों में समाप्त करेगा ?
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18 days/दिन
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20 days/दिन
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25 days/दिन
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90 days/दिन
A
Correct answer
Explanation
Let A alone take x days. Then B and C each take 5x days (since they take 5 times A's time). Combined rate: 1/x + 1/(5x) + 1/(5x) = 1/x + 2/(5x) = 7/(5x). Time together = 5x/7 = 15 days. Solving: x = 21 days. However, this doesn't match the options. Let's re-interpret: if B and C together take 5 times A (i.e., their combined time is 5x), then A's rate + combined rate of B&C = 1/x + 1/(5x) = 6/(5x) = 1/15, giving x = 18 days. Option D (90 days) would be correct if only B or only C worked, not all three together.