A, B, and C can complete a certain task in 20, 30, and 60 days, respectively. How many days will it take for A to finish the work if he receives help from B and C every third day?
Show answer & explanation
Correct answer: A
Explanation
The correct answer is option 1 i.e. 15 days.
A’s rate = 1/20
B’s rate = 1/30
C’s rate = 1/60
Every 3rd day B and C help A:
Day 1: A → 1/20
Day 2: A → 1/20
Day 3: A + B + C → 1/20 + 1/30 + 1/60 = 1/20 + 1/20 = 1/10
Work in 3 days = 1/20 + 1/20 + 1/10 = 1/5
Whole work in 3 × 5 = 15 days