Discussion of Question with ID = 008 under Time-and-Work

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A and B can together complete a job in 21 days. A can alone complete it in 28 days. How long would B alone take to finish the job?


84 days.


85 days.


83 days.


87 days.

Ans: a

One day work of A + B is $1/21$. One day work of A is $1/28$. So one day work of B, say, $1/y$ = $1/21$ - $1/28$. Solving, we get y = 84 days.

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