enigma123 wrote:

Machine A can complete a certain job in x hours. Machine B can complete the same job in y hours. If A and B work together at their respective rates to complete the job, which of the following represents the fraction of the job that B will not have to complete because of A's help?

A) (x – y)/(x + y)

B) x/(y – x)

C) (x + y)/(xy)

D) y/(x – y)

E) y/(x + y)

Machine A can complete a job in X hours.

Machine B can complete a job in Y hours.

Thus, A and B working together can complete a job in \(\frac{xy}{x+y}\) hours.

what fraction of the job that B will not have to complete because of A's help means that A will complete the whole work that requires \(\frac{xy}{x+y}\) hours

Machine A's rate=1/x

W=R X T

W = \(\frac{1}{x}\) X \(\frac{xy}{x+y}\)

W = \(\frac{y}{x + y}\)

HENCE, E

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