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A and B can complete a work working individually in 60 days and 40 days respectively. Both start working simultaneously on the work simultaneously, but B did not work on the last 4 days. Find the total number of days taken for the work to be completed.

A. 24
B. 25
C. 26.4
D. 28.2
E. 30
Rate of A = 1/60
Rate of B = 1/40

Combined rate of A and B = 1/60 + 1/40 = 5/120 =1/24
Work done by A alone = 4/60 = 1/15
Remaining work to be done by A and B = (1-1/15) = 14/15
The number of days taken by A + B together =(14/15)*(24/1) = 22.4 days

Total days needed = 22.4 + 4 = 26.4 days

Answer:C
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Bunuel Why setting the following equation doesn't work?

(x-4)*(1/24) + 4*(1/60) = 1

x=tot amount of days
1/24= rate A + B
1/60 = rate A

Thank you
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Bunuel Why setting the following equation doesn't work?

(x-4)*(1/24) + 4*(1/60) = 1

x=tot amount of days
1/24= rate A + B
1/60 = rate A

Thank you

You've done everything right. You should get 132/5 = 26.4 as an answer, which is correct.
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Bunuel
A and B can complete a work working individually in 60 days and 40 days respectively. Both start working simultaneously on the work simultaneously, but B did not work on the last 4 days. Find the total number of days taken for the work to be completed.

A. 24
B. 25
C. 26.4
D. 28.2
E. 30

Start from the last 4 days. A works alone at this time and does 4 * (1/60) = 1/15th of the work

So the rest of the 14/15th work, both have to do together.

Combined rate of work = 1/60 + 1/40 = 1/24th of the work

Time taken = Work/Rate = (14/15) / (1/24) = 22.4 days

So total number of days = 22.4 + 4 = 26.4 days

Answer (C)
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