P alone can complete a work in 15 days and Q alone can complete the same work in 12 days. They start the work together but after 3 days P leaves the work. How much time will Q take to finish the remaining work?
Answer & explanation
Correct answer: option 4
efficiency ∝ $\frac{1}{time}$
P : Q
time 15 : 12
efficiency 4 : 5 ⇒ total = 9
Total work = LCM of 12, 15 = 60
Work done by P and Q together in 3 days = efficiency of P & Q x 3
= 9 x 3 = 27
Work left = 60 - 27 = 33
Time taken by Q alone to complete the remaining work = $\frac{remaining\;work}{efficiency}$
= $\frac{33}{5}$ = 6.6 days