Question by Summer Clouds - Discuss with MathYouLike

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31/08/2017 at 08:56

A stack of loads must be transported. If Ann does the job alone, it will take one hour. If Ben does the job alone, it will take two hours. How long will it take if Ann and Ben do the job together? (A) 30 minutes (B) 40 minutes (C) 1 hour (D) 1.5 hours (E) 3 hours

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Dao Trong Luan 31/08/2017 at 09:14

In 1h Ann do the work part number is:

1 : 1 = 1 [job]

In 1h Ben do the work part number is:

1 : 2 = 1/2 [job]

In 1h Ann and Ben do the work part number is:

1 + 1/2 = 3/2 [job]

The two of you do the work that will be done after the time is:

1 : 3/2 = 2/3 [hour]

2/3h = 40minutes

So choose B
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