Question

A can do a piece of work in 20 days and B in 30 days. They began to work together but A left
after some days. B finished the remaining work in 10 days. After how many days did A leave?
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Answer 1

Answer:

b alone takes 30 days to finish the entire work,

And it is mentioned that b completed the “remaining work" alone in 10 days.

It implies that the “remaining work" was 10/30 = 1/3 rd of the total work that b finished alone.

Which further implies that together, a and b must have finished 1 - 1/3 = 2/3 rd of the total work together.

Now, a and b together can finish 1/20 + 1/30 of work in 1 day = 1/12 th of total work in 1 day.

Hence, to complete 2/3 rd of the work or 8/12 of the work together, they will take 8 days.

Hence, a must have left after 8 days of working with b, and then b did the remaining work in 10 days.

Step-by-step explanation:

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