RRB NTPC · Question 63
X and Y together can complete a piece of work in 12 days, Y and Z can do it 18 days and X and Z can complete the same work in 15 days. If X, Y and Z can together complete the work, approximately how many days will be required to complete the work?
Show answer & explanation
Answer: (D) 10
Explanation
Adding the pair rates: 2(X + Y + Z) = 1/12 + 1/18 + 1/15 = 37/180, so X + Y + Z = 37/360 per day. Time = 360/37 ≈ 9.7, about 10 days.