# A and B can together finish a work in 30 days. They worked together for 20 days and then B left. After another 15 days, A finished the remaining work.

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A and B can together finish a work in 30 days. They worked together for 20 days and then B left. After another 15 days, A finished the remaining work. In how many days A alone can finish the job?
1. 45 days
2. 30 days
3. 40 days
4. 35 days

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Correct Answer - Option 1 : 45 days

Given:

A and B together finish work = 30 days

B left the work = 20 days after working together

Remaining work finished by A = 15 days

Formula used:

Efficiency = Total work/Time

Calculation:

Let the total work done by A and B be 30 units

According to the question

Total work done by A and B in 20 days = 20 units

Remaining work = (30 - 20) units = 10 units

Since, B left after 20 days and remaining work completed by A alone in 15 days

Efficiency of A = 10/15 = (2/3) units per day

Time taken by A to finish job alone = [30/(2/3)]

⇒ (30 × 3)/2

⇒ 45 days

∴ A can alone finish the job in 45 days.