How many days B alone does it work?

A does 80 % of a work in 20 days. He then calls in B and together they finish the remaining work in 3 days. How long B alone would take to do the whole work:

  1. 23 days
  2. 37 days
  3. 75/2 days
  4. 40 days
Monis Rasool Professor Asked on 25th October 2015 in Maths.
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1 Answer(s)

Answer: (3) 75/2 days

A can 80% of a work = 20 days
Then, the whole work is done by A = 20 x 5/4
= 5 x 5 = 25 days

Remaining work = 1 – 4/5
= (5 – 4)/5 = 1/5
Remaining work done by A and B = 3 days
Then, whole work done  by A and B = 3 x 5 = 15 days

A can do the work in a day = 1/25 days
(A + B) can the work in a day = 1/15 days

Then, B can do the work in a day = 1/15 – 1/25
= (5 – 3)/75
= 2/75
Therefore, B can do the whole work = 75/2 days.

Hence, the answer is (3) 75/2 days.

Anurag Mishra Professor Answered on 25th October 2015.
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