A can do a work in 12 days and B in 18 days. If they work on it together for 4 days, then what fraction of work is left?
- A4/9
- B5/9
- C5/36
- D7/36
Solution & Step-by-step Explanation
Let the total work be the LCM of 12 and 18, which is 36 units.
Efficiency of A =
12
36
=3 units/day
Efficiency of B =
18
36
=2 units/day
Combined efficiency of A and B = 3+2=5 units/day
Work done by both working together in 4 days:
Work done=5×4=20 units
Remaining work:
Remaining work=36−20=16 units
Fraction of work left:
Fraction left=
36
16
=
9
4
Efficiency of A =
12
36
=3 units/day
Efficiency of B =
18
36
=2 units/day
Combined efficiency of A and B = 3+2=5 units/day
Work done by both working together in 4 days:
Work done=5×4=20 units
Remaining work:
Remaining work=36−20=16 units
Fraction of work left:
Fraction left=
36
16
=
9
4