Question

A can do a piece of work in 20 days while B can do it in 15 days. With the help of C, they finish the work in 5 days. In what time would C alone do it?
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Answer 1

Answer:

answer is 12

Step-by-step explanation:

A can do the work in 20 days

⇒ 1 day = 1/20 of the work

B can do the work in 15 days

⇒ 1 day = 1/15 of the work

Find the amount of work A and B can complete in a day:

1 day = 1/20 + 1/15 = 7/60

Find the amount of work c can complete in a day:

a + b + c can complete the work in 5 days

⇒ 1 day = 1/5 of the work

C alone

⇒ 1 day = 1/5 - 7/60 = 1/12

Find number of days c needs to complete the work:

1/12 of the work = 1 day

12/12 of the work = 1 x 12 = 12 days

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