Question

A can finish a piece of work in 30 days. He
worked alone for 3 days and B joined him. To-
gether they could finish the remaining work in 9
days. In how many days B alone can finish the
same piece of work ?​

Answer 1

Answer:

A can finish a piece of work in 30 days. He worked alone for 6 days and B joined him. Together they could finish the remaining work in 9 days. In how many days can B alone can finish the same piece of work?

A- 30 days for full work; 1 day: 1/30 work.

6 days: 6/30 work done; 6/30 is 1/5.

Remaining work:4/5

Together done in 9 days.

Together in one day: (4/5)÷9=4/45=8/90

Done by A in one day: 1/30=3/90

Done by B in one day=(8/90)-(3/90)=(8–3)/90=5/90=1/18

B does 1/18 work per day: so 18 days required to complete work alone.

Ans: 18 days.

Alternate method: 6, 9 and 30 are numbers used in problem description. So, let us take common multiple; 90 is one such number.

We consider full work as 90 units.

A does 90 units in 30 days.; so 3 units per day.

In 6 days A does6×3=18 units.

Remaining work =72 units done by A and B together in 9 days.; 8 units per day.

Out of 8 units per day together, A does 3 units.

So, B does 5 units per day.

At 5 units per day, B needs 18 days to complete 90 units of work (full work).

Ans: 18 days.

Step-by-step explanation:

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Answer 2

Step-by-step explanation:

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