Skip to main contentSkip to solution

A group of NN people worked on a project. They finished 35%35 \% of the project by working 77 hours a day for 1010 days. Thereafter, 1010 people left the group and the remaining people finished the rest of the project in 1414 days by working 1010 hours a day. Then the value of NN is

Solution

✅ Correct Option: 1

We have a classic work and time problem where initially N people work together, later 10 people leave so only (N-10) people continue, and we need to find the total number of people N.


Phase 1: Initial work period

People: N

Time: 7 hours/day for 10 days = 70 hours total

Work completed: 35% of the project


Phase 2: After 10 people left

People: (N-10)

Time: 10 hours/day for 14 days = 140 hours total

Work completed: Remaining 65% of the project


The amount of work done per person per hour remains constant throughout the project.

This gives us the formula:

People×HoursWork=constant\tfrac{\text{People} \times \text{Hours}}{\text{Work}} = \text{constant}

If each person works at the same rate, then doubling the people or doubling the hours should double the work output.


Since the work rate is constant:

N×7035=(N−10)×14065\dfrac{N \times 70}{35} = \dfrac{(N-10) \times 140}{65}

Left side: N people × 70 hours ÷ 35% work = work rate

Right side: (N-10) people × 140 hours ÷ 65% work = same work rate


N×7035=(N−10)×14065\dfrac{N \times 70}{35} = \dfrac{(N-10) \times 140}{65}

The left side simplifies to:

70N35=2N\dfrac{70N}{35} = 2N

Our equation becomes:

2N=(N−10)×140652N = \dfrac{(N-10) \times 140}{65}

2N×65=(N−10)×1402N \times 65 = (N-10) \times 140

130N=140N−1400130N = 140N - 1400

130N−140N=−1400130N - 140N = -1400

−10N=−1400-10N = -1400

N=140N = 140


The original group had 140 people working on the project.

Keyboard Shortcuts

  • Left arrow: Previous question
  • Right arrow: Next question
  • S key: Jump to solution
  • Q key: Jump to question