Jack can do a piece of work in 30 days. Ryan can do this work in 14 days. Jack started the work alone. After how many days should Ryan join him, so that the work is finished in 15 days ?
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3 i.e. 8 days
According to the question
Jack × 30 days = Ryan × 14 days
The effeciency of
Jack : Ryan = 7 : 15
Let Ryan join Jack after D days
Total work = 7 × 30 = 210
Jack × D + (Jack + Ryan) × (15 - D) = 210
7D + (7 + 15) × (15 - D) = 210
7D + 22 × (15 - D) = 210
7D + 330 - 22D = 210
15D = 330 - 210 = 120
D = 120/15 = 8 days