A can do a work in 20 days and B in 50 days. If they work on it together for 5 days, then what fraction of work is left?
- A20
13
- B3
1
- C6
1
- D9
2
Solution & Step-by-step Explanation
Let's find the total work by taking the LCM of 20 and 50, which is 100 units.
Efficiency of A=
20
100
=5 units/day
Efficiency of B=
50
100
=2 units/day
Combined efficiency of A and B=5+2=7 units/day.
Work completed by both in 5 days:
Work done=7×5=35 units
Remaining work:
Work left=100−35=65 units
Fraction of work left:
Fraction left=
100
65
=
20
13
Efficiency of A=
20
100
=5 units/day
Efficiency of B=
50
100
=2 units/day
Combined efficiency of A and B=5+2=7 units/day.
Work completed by both in 5 days:
Work done=7×5=35 units
Remaining work:
Work left=100−35=65 units
Fraction of work left:
Fraction left=
100
65
=
20
13