X is able to do a piece of work in 8 days and Y can do the same work in 12 days. If they can work together for 3 days, what is the fraction of work left?  Choose the correct choice:
A) 8 / 5
B) 6 / 5
C) 7 / 5
D) 3 / 5
E) 4 / 5

Rationale: "explanation : amount of work x can do in 1 day = 1 / 8 amount of work y can do in 1 day = 1 / 12 amount of work x and y can do in 1 day = 1 / 8 + 1 / 12 = 5 / 24 amount of work x and y can together do in 3 days = 3 × ( 5 / 24 ) = 5 / 8 fraction of work left = 1 – 5 / 8 = 3 / 5 answer : option d"
Answer: D