Two persons X and Y can do a piece of work in n days. If X alone can complete the work in (n + 3) days and Y alone can do the work in (n + 12) days, find the value of n.
A6 ✓ Correct
B10
C7
D5
Correct answer: (A) 6
Explanation
n = 6.
1/(n + 3) + 1/(n + 12) = 1/n.
Cross-multiplying: n(n + 12) + n(n + 3) = (n + 3)(n + 12).
2n^2 + 15n = n^2 + 15n + 36.
n^2 = 36, so n = 6.
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