A can do a work in 20 days and B in 30 days. They work together for 7 days and then both leave. Then C alone finishes the remaining work in 10 days. In how many days will C alone finish the whole work? MCQ with Answer and Explanation
A can do a work in 20 days and B in 30 days. They work together for 7 days and then both leave. Then C alone finishes the remaining work in 10 days. In how many days will C alone finish the whole work?
A. 25 days
B. 40 days
C. 30 days
D. 24 days
Answer: Option D
Solution (By JKSSB Mock Tests)
Total work = LCM(20, 30) = 60 units. Efficiency of A = 3, B = 2. Combined efficiency = 5 units/day. In 7 days, work done = 7 * 5 = 35 units. Remaining work = 60 - 35 = 25 units. C's efficiency = 25 units / 10 days = 2.5 units/day. Days for C to complete total work = 60 / 2.5 = 24 days.
Explanation:
Let efficiency of B = 2, then efficiency of A = 3. Total work = Efficiency of A * Time of A = 3 * 12 = 36 units. Time taken by B = 36 / 2 = 18 days.
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