A can do a work in 21 days and B in 42 days. If they work on it together for 7 days, then what fraction of work is left?
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e. 1/2
Let the total work be 42 units
Efficiancy of A = 2 units/day
Efficiancy of B = 1 unit/day
A/Q
Work done in 7 days = (2 + 1) × 7 = 21 units
Left work = 42 - 21 = 21 units
Required fraction of work = 21/42 = 1/2