7. A can do a piece of work in 14 days which B can do it in 21 days. They begin together but 3 days
before the completion of the work. A leaves off. Find the total number of days taken to finish work.
Answers
Answer:
If A can do the wrok in 14 days, his work per day = 1/14
if B can do the work in 21 days, his work per day = 1/21
if A and B work together, work per day = (1/14)+(1/21) = 5/42
Hence work will be completed, if and B work together = 42/5 = [ 8+(2/5) ] days.
If A leaves 3 days before completion of work, hence they worked together for 5 days.
Hence completed work in 5 days = 5×(5/42) = 25/42
remaining work = 1 - (25/42) = 17/42
If A can do the wrok in 14 days, his work per day = 1/14
if B can do the work in 21 days, his work per day = 1/21
if A and B work together, work per day = (1/14)+(1/21) = 5/42
Hence work will be completed, if and B work together = 42/5 = [ 8+(2/5) ] days.
If A leaves 3 days before completion of work, hence they worked together for 5 days.
Hence completed work in 5 days = 5×(5/42) = 25/42
remaining work = 1 - (25/42) = 17/42
Hence no. of days required for B to complete = 17/42 = 8.5 days
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