Question

A, B and C can do a piece of work in 20, 30 and 60 days respectively. In how many days can A do the work if he is assisted by B and C on every third day?

• A. 12
• B. 15
• C. 18
• D. 20
• E. 10

Hint:

For rotational or assisted work, find the total work done in one complete "cycle" (in this case, 3 days).

Answer 1

The Correct Option is B

Step 1: Analyse options.
- 1 day work: A = 1/20, B = 1/30, C = 1/60. - Day 1: A works (1/20). Day 2: A works (1/20). - Day 3: A+B+C work: $1/20 + 1/30 + 1/60 = (3+2+1)/60 = 1/10$. - 3 days work total = $1/20 + 1/20 + 1/10 = 1/5$. - Time to complete work (1) = $3 \text{ days} \times 5 = 15 \text{ days}$.
Step 2: Conclusion.
The work will be completed in 15 days. Final Answer: (b) 15