Question

A alone can complete the work in 20 days and B alone can complete the work in 30 days. They both worked for 7 days. The fraction of work remained after 7 days.
1. 8/9
2. 7/11
3. 5/12
4. 1/9

Answer 1

Correct Answer - Option 3 : 5/12

Calculation:

A's 1 days work = 1/20

B's 1 days work = 1/30

(A + B)'s 1 days work = 1/20 + 1/30 = 5/60 = 1/12

(A + B)'s 7 days work = 7 × 1/12 = 7/12

∴ Fraction of work remained after 7 days = 1 - 7/12 = 5/12