A alone can finish a work in X days. B alone can finish the same work in X+5 days. Together, they take 6 days to complete the work. Find X

A. 12
B. 8
C. 10
D. 9

Part of work completed by A in a day = 1/X Part of work completed by B in a day
= 1/(X+5) (1/X)+(1/(X+5)) = 1/6 (2X+5)/(X²+5X) = 1/6 X²+5X = 6(2X+5) X²-7X-30=0 Solving, X=10

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