Student: Ravi can do a piece of work in 30 days while Prakash can do it in 40 days. In how many days will they finish it together?\nOptions:\n(A) 17 1/7\n(B) 17 1/9\n(C) 17 1/2\n(D) 17 1/7\n(E) 17 1/5.
Another student: Let's say, hmmm...

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1/30 + 1/40 = 7/120\n120/7 = 17 1/7 days Final answer: (A).
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