Question

79
19. A and B working together can finish a job in 3
hours, while A can finish the job alone in 5 hours.
What fraction of the job does A do, when A and B
work together?
A) 1/5
B) 3/5
C) 2/5 D) 3/8 E) 1/5​

Answer 1

Answer:

Let a and b be the amount of time it takes A and B, respectively, to finish the job alone. Then:

1/a + 1/b=1/3

a=5, so:

1/5 + 1/b=1/3

1/b=1/3 - 1/5=5-3/15=2/15

b=15/2 hours alone

So, in doing one job, A does 3/5 of the work, and B does 3 x 2/15=6/15=2/5 of the work

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