Student: A tyre has two punctures. The first puncture along would have made the tyre flat in 9 minutes and the second alone would have done it in 6 minutes. If air leaks out at a constant rate, how long does it take both the punctures together to make it flat?\nOptions:\n(A) 1 1⁄2 minutes\n(B) 3 1⁄2 minutes\n(C) 3 3⁄5 minutes\n(D) 4 1⁄4 minutes\n(E) None of these.
Another student: Let's say, hmmm...

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1 minute’s work of both the punctures = (1⁄9 + 1⁄6) = 5⁄18\nSo, both the punctures will make the tyre flat in 18⁄5 = 33⁄5 min. Final answer: (C).
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