in How Many Days can A Alone do it? If

A and B can do a piece of work in 72 days. B and C can do it in 120 days. A and C can do it in 90 days. In what time can A alone do it?

  1. 80 days
  2. 100 days
  3. 120 days
  4. 150 days
vijay Professor Asked on 5th August 2015 in Maths.
Add Comment
  • 1 Answer(s)

    Answer: (3) 120 days
    Explanation:-
    A and B can do a piece of work = 72 days
    Therefore, A  and B  can do a piece of work in a day = 1/72.

    B and C can do it = 120 days
    Therefore, B and C can it in a day = 1/120

    A and C can do it = 90 days
    Therefore, A and C can do in a day = 1/90

    Then, A , B  & C can do it in a day = (1/72 + 1/120 + 1/90 ) / 2
    = (5 + 3 + 4)/360 x 2
    = 12 /360 x 2
    = 1/30 x 2
    = 1/60

    Then, A alone can do it in a day  = 1/60 – 1/120
    = (2 – 1 ) /120
    = 1/120
    Therefore, A alone can do complete the work = 120 days.

    Hence, the answer is (3) 120 days.

    Anurag Mishra Professor Answered on 6th August 2015.
    Add Comment

    Your Answer

    By posting your answer, you agree to the privacy policy and terms of service.