1.  X can completed a job in 12 days. If X and Y work together, they can complete the job in 6 days, Y alone can complete the job in:
A. 10 days
B. 12 days
C. 15 days
D. 18 days

Answer: Option C

Explanation:

X's 1 day's work = 1/12

(X + Y)' s 1 day's work = 3/20

∴ Y's 1 day's work = (3/20) - (1/12) = 4/60 = 1/15

∴ Number of day's taken by Y to complete the work = 15 days