A can do a work in 15 days and B in 20 days. If they work on it together for 4 days, then the fraction of the work that is left is : Choices.
A) 7/14 B) 7/15 C) 7 D) 8/15 E) 8
A's 1 day's work = 1/15   B's 1 day's work = 1 /20   (A + B)'s 1 day's work = ( 1/15 + 1/20 ) = 7 /60   (A + B)'s 4 day's work = (4*7)/60 = 7/15   Therefore, Remaining work = ( 1 - 7/15) = 8/15   So correct answer is 8/15
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A can do a work in 15 days and B in 20 days. If they work on it together for 4 days, then the fraction of the work that is left is :