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John takes twice as much time as Jack to finish a job. Jack and Jim together take one-thirds of the time to finish the job than John takes working alone. Moreover, in order to finish the job, John takes three days more than that taken by three of them working together. In how many days will Jim finish the job working alone?

Entered answer:

Solution

✅ Correct Answer: 4

We'll break down this work-rate problem using the relationships between the workers' efficiencies.

Let us define variables clearly:

  • Let Jack take J days to finish the job alone
  • John takes twice as much time as Jack, so John takes 2J days
  • We need to find how many days Jim takes alone

Work rate = 1/time, so if someone takes 'd' days, their rate is 1/d jobs per day.

From the given information:

  • Jack's rate = 1J\dfrac{1}{J} jobs per day
  • John's rate = 12J\dfrac{1}{2J} jobs per day

Second condition: Jack and Jim together take one-third the time John takes alone.

  • John alone takes 2J days
  • Jack and Jim together take 2J3\dfrac{2J}{3} days
  • Combined rate of Jack and Jim = 32J\dfrac{3}{2J} jobs per day

Since Jack and Jim's combined rate = Jack's rate + Jim's rate:

32J=1J+Jim’s rate\dfrac{3}{2J} = \dfrac{1}{J} + \text{Jim's rate}

Jim’s rate=32J−1J=32J−22J=12J\text{Jim's rate} = \dfrac{3}{2J} - \dfrac{1}{J} = \dfrac{3}{2J} - \dfrac{2}{2J} = \dfrac{1}{2J}

Therefore, Jim takes 2J days to finish the job alone.


All three working together:

  • Combined rate = 1J+12J+12J=1J+22J=1J+1J=2J\dfrac{1}{J} + \dfrac{1}{2J} + \dfrac{1}{2J} = \dfrac{1}{J} + \dfrac{2}{2J} = \dfrac{1}{J} + \dfrac{1}{J} = \dfrac{2}{J}
  • Time taken together = J2\dfrac{J}{2} days

The condition states: John takes 3 days more than all three working together.

2J=J2+32J = \dfrac{J}{2} + 3

2J−J2=32J - \dfrac{J}{2} = 3

4J−J2=3\dfrac{4J - J}{2} = 3

3J2=3\dfrac{3J}{2} = 3

J=2J = 2


Since J = 2:

  • Jack takes 2 days
  • John takes 4 days
  • Jim takes 2J = 4 days

Therefore, Jim will finish the job in 4 days working alone.

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