Question

A can complete a piece of work in 7 days and B can complete the same work in 12 days. A and B worked together for 3 days. C alone completed the remaining work in 9 days will C take to complete the same work entirely?
1. 21
2. 35
3. 28
4. 14

Answer 1

Correct Answer - Option 3 : 28

Given:

A's 1 day's work = 1/7

B's 1 day's work = 1/12

Calculation:

(A + B)'s 1 day's work = 1/7 + 1/12 = 19/84

(A + B)'s 3 days work = 3 × 19/84 = 19/28

Remaining work = 1 - 19/28 = 9/28

Number of days in which C alone can complete work = 28/9 × 9 = 28 days

∴ C alone can complete work in 28 days.