A takes 84 hours to finish a work. B completes the same work in one-fourth of the time taken by A. What fraction of work will they complete in 12 hours?
- A21
5
- B21
11
- C7
1
- D7
5
Solution & Step-by-step Explanation
Time taken by A =84 hours.
Time taken by B =
4
1
×84=21 hours.
Work done by A in 1 hour =
84
1
Work done by B in 1 hour =
21
1
Combined work done by A and B in 1 hour:
84
1
+
21
1
=
84
1+4
=
84
5
Work done by both in 12 hours:
Fraction of work=12×
84
5
=
7
5
Time taken by B =
4
1
×84=21 hours.
Work done by A in 1 hour =
84
1
Work done by B in 1 hour =
21
1
Combined work done by A and B in 1 hour:
84
1
+
21
1
=
84
1+4
=
84
5
Work done by both in 12 hours:
Fraction of work=12×
84
5
=
7
5