A is 20% less efficient than B. If A can complete a work in 15 days, in how many days will B complete it? MCQ with Answer and Explanation

A is 20% less efficient than B. If A can complete a work in 15 days, in how many days will B complete it?

A. 12 days

B. 11 days

C. 9 days

D. 10 days

Answer: Option A

Solution (By JKExamLibrary)

Let efficiency of B = 5, then efficiency of A = 4. Total work = Efficiency of A * Time of A = 4 * 15 = 60 units. Time taken by B = 60 / 5 = 12 days.

This question belongs to: Maths Time and Work

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Question #1 Report Error

A can build a wall in 20 days, while B can destroy it in 30 days. If they work on alternate days starting with A, in how many days will the wall be completely built?

A. 116 days

B. 120 days

C. 115 days

D. 113 days

View Answer & Solution Discuss

Correct Answer: Option C

Explanation:
Total work = LCM(20, 30) = 60 units. Efficiency of A = +3, B = -2. In 2 days (A then B), net work done = 3 - 2 = 1 unit. We need to reach 60 units. Since A can add 3 units on his turn, we find when work reaches 60 - 3 = 57 units. 57 units will be done in 57 * 2 = 114 days. On the 115th day, A works and completes 3 units, making the total work 57 + 3 = 60 units. So, the wall is built in 115 days.

This question belongs to: Maths Time and Work