Time and Work


  1. A and B can complete a job in the 24 days working together. A alone can complete it in 32 days. Both of them worked together for 8 days and then A left. The number of days B will take to complete the remaining job is









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    Let B will take N days to complete the remaining job.
    According to the question
    (1/A) + (1/B) = 1/24 and 1/A = 1/32
    ∴ 1/B = (1/24) - (1/32) = 1/96
    ⇒ B = 96 days

    According to the question,
    8[(1/A) + (1/B)] + N x (1/B) = 1

    Correct Option: C

    Let B will take N days to complete the remaining job.
    According to the question
    (1/A) + (1/B) = 1/24 and 1/A = 1/32
    ∴ 1/B = (1/24) - (1/32) = 1/96
    ⇒ B = 96 days

    According to the question,
    8[(1/A) + (1/B)] + N x (1/B) = 1
    ⇒ 8 x (1/24) + (N/96) = 1
    ⇒ (1/3) + (N/96) = 1
    ⇒ N/96 = 1 -1/3
    ∴ N = (2 x 96)/3 = 64
    Hence, B complete the remaining job in 64 days


  1. 90 men are engaged to do piece of work in 40 days but it is found that in 25 days, 2/3 work is complete. How many men should be allowed to go off, so that the work finished in time ?









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    Let N men are allowed to go off,
    M1= 90, D1 = 25, D2 = 15
    W1 = 2/3, W2 = 1 - (2/3) = 1/3
    M2 = 90 - N
    According to the formula, M1D1W2 = M2D2W1
    ⇒ (90 x 25) (1/3) = (90 - N) x 15 x (2/3)

    Correct Option: B

    Let N men are allowed to go off,
    M1= 90, D1 = 25, D2 = 15
    W1 = 2/3, W2 = 1 - (2/3) = 1/3
    M2 = 90 - N
    According to the formula, M1D1W2 = M2D2W1
    ⇒ (90 x 25) (1/3) = (90 - N) x 15 x (2/3)
    ⇒ 90 x 25 x (1/3) = 10(90 - N)
    ⇒ 75 = 90 - N
    ∴ N = 90 - 75 = 15



  1. 20 workers working for 5 h per day complete a work in 10 days. If 25 workers are employed to work 10 h per days, what is the time required to complete the work ?









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    Given, M1= 20, M2 = 25, T1 = 5, T2 = 10, D1 = 10 and D2 = ?
    According to the formula,
    M1T1D1= M2T2D2

    Correct Option: A

    Given, M1= 20, M2 = 25, T1 = 5, T2 = 10, D1 = 10 and D2 = ?
    According to the formula,
    M1T1D1= M2T2D2
    ⇒ 20 x 5 x 10 = 25 x 10 x D2
    ∴ D2 = 20 x 5 x 10/25 x 10 = 4 days


  1. A, Band C can do a piece of work individually in 8, 12 and 15 days, respectively. A and B start working but A quits after working for 2 days. After this, C joins B till the completion of work. In how many days will the work be completed ?









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    Work done by A and B in 1 day
    = (1/8) + (1/12) = 5/24
    2 day's work of A and B = 10/24
    After 2 day's A left the work
    ∴ Remaining work = 1 - (10/24) = 14/24
    One day work of B and C together = (1/12) + (1/15) = 9/60
    So, the number of days required by B and C to finish work
    = (14/24) / (9/60) = (14/24) x (60/9) = 35/9

    Correct Option: A

    Work done by A and B in 1 day
    = (1/8) + (1/12) = 5/24
    2 day's work of A and B = 10/24
    After 2 day's A left the work
    ∴ Remaining work = 1 - (10/24) = 14/24
    One day work of B and C together = (1/12) + (1/15) = 9/60
    So, the number of days required by B and C to finish work
    = (14/24) / (9/60) = (14/24) x (60/9) = 35/9
    ∴ Total days to complete the work = 2 + (35/9) = 53/9 = 58/9 days



  1. A and B together can complete a work in 3 days. They started together but after 2 days, B left the work. If the work is completed after 2 more days, B alone could do the work in how many days ?









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    (A + B)'s 2 day's work = 2 x (1/3) = 2/3
    Remaining work = 1 - (2/3) = 1/3
    A will complete 1/3 work in 2
    A will complete 1 work in 6

    Correct Option: B

    (A + B)'s 2 day's work = 2 x (1/3) = 2/3
    Remaining work = 1 - (2/3) = 1/3
    A will complete 1/3 work in 2
    A will complete 1 work in 6
    A's 1 days work = 1/6
    B's 1 day's work = (1/3) - (1/6) = 1/6
    ∴ B will take 6 days to complete the work alone.