and together we can complete a work in 12 days. A alone can complete it in 20 days If now does the work for half a day dally Then in how many days and Will we complete the work together ?

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15 days

20 days

45 days

30 days

answer is A.

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Detailed Solution

Concept: A and B can finish a task in 12 days when working together. Determine how much work A and B accomplished in one day, X. The task can be finished by A alone in 20 days. Only use A say Y to calculate the amount of work completed in a day.
To find the quantity of work that B can complete in a single day, subtract y from x. Exchange z to learn how many days B alone will need to complete the task, let's say a. If he works half a day, then B will have twice as many days, let's say two. Add

and

a to get the required value.
We are given

and

together we can complete a work in 12 days.
The work done by

and

together in a day will be

We are also given A alone to finish the work in 20 days.
The work done by only

in a day will be

Subtract

from

to get the work done by only B in a day.
B

Therefore, B alone can finish

of the work in one day.
This means B alone takes 30 days to finish the total work.
When B works half a day then he will take

days to finish the total work.
When A works full day and B works half day then the work which will be finished in one day will be

A and B can together finish

th of the work in one day, this means when A works full day and B works half day then it takes 15 days to finish the total work.
Hence, the correct answer is Option (1).

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