Time and Work

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  1. A and B can do a piece of work in 12 days. B and C in 15 days. C and A in 20 days. A alone can do the work in ?








  1. View Hint View Answer Discuss in Forum

    ∵ [(A + B) + (B + C) + (C + A)]'s 1 day's work = (1/12 + 1/15 + 1/20) = 1/5
    ⇒ 2(A + B + C)'s 1 days work = 1/5
    ⇒ (A + B + C)'s 1 day's work = 1/10
    &rArr A's 1 day's work = (1/10 - 1/15) = 1/30
    ∴ A alone can finish it in 30 days.

    Correct Option: C

    ∵ [(A + B) + (B + C) + (C + A)]'s 1 day's work = (1/12 + 1/15 + 1/20) = 1/5
    ⇒ 2(A + B + C)'s 1 days work = 1/5
    ⇒ (A + B + C)'s 1 day's work = 1/10
    &rArr A's 1 day's work = (1/10 - 1/15) = 1/30
    ∴ A alone can finish it in 30 days.

  1. A and B can do a piece of work in 18 days, B and C in 24 days, A and C in 36 days. In what time can they do it all working together ?








  1. View Hint View Answer Discuss in Forum

    (A + B)'s 1 day's work = 1/18
    (B + C)'s 1 day's work = 1/24
    (A + C)'s 1 day's work = 1/36
    Adding 2 (A + B + C)'s 1 day's work = (1/18 + 1/24 + 1/36) = 1/8

    Correct Option: C

    (A + B)'s 1 day's work = 1/18
    (B + C)'s 1 day's work = 1/24
    (A + C)'s 1 day's work = 1/36
    Adding 2 (A + B + C)'s 1 day's work = (1/18 + 1/24 + 1/36) = 1/8
    ∴ (A + B + C)'s day's work = 1/16
    Hence, all working together can finish it in 16 days.

  1. Ajit is 3 times as efficient as Bablu, then the ratio of number of days required by each to work alone, completely?








  1. View Hint View Answer Discuss in Forum

    Efficiency of Ajit : Bablu = 3 : 1
    No. of days 1 : 3

    Correct Option: B

    Efficiency of Ajit : Bablu = 3 : 1
    No. of days 1 : 3

  1. A and B can together do a piece of work in 15 days. B alone can do it 20 days. In how many days can A alone do it ?








  1. View Hint View Answer Discuss in Forum

    A's 1 day's work = (1/15 - 1/20) = 1/60

    Correct Option: D

    A's 1 day's work = (1/15 - 1/20) = 1/60
    ∴ A alone can finish it in 60 days.

  1. 20 persons completed 1/3rd of the work in 12 days. How many more person are required to finish the rest work in next 12 days?








  1. View Hint View Answer Discuss in Forum

    Work done = 1/3
    Remaining work = 2/3
    So for double work in same days we need double number of people i.e. 40.

    Correct Option: A

    Work done = 1/3
    Remaining work = 2/3
    So for double work in same days we need double number of people i.e. 40.

    So, 20 men will be increased.