Solve for Time: 3 Workers vs 4 Workers Painting Rate Problem

Inverse Proportions with Work Rates

3 workers finish painting a room in 4 hours.
How many hours will it take 4 workers to paint the same room?

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Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

3 workers finish painting a room in 4 hours.
How many hours will it take 4 workers to paint the same room?

2

Step-by-step solution

To solve this problem, we'll follow these steps:

  • Step 1: Calculate the work rate for the 3 workers.
  • Step 2: Determine the equivalent rate when 4 workers are involved.
  • Step 3: Calculate the time required for 4 workers using the combined rate.

Let's go through each step in detail:

Step 1: Calculate the work rate for the 3 workers.
If 3 workers can complete the task in 4 hours, then their combined work rate is:

Rate of 3 workers=1 room4 hours \text{Rate of 3 workers} = \frac{1 \text{ room}}{4 \text{ hours}}

Therefore, the rate of 1 worker is:

Rate of 1 worker=13×1 room4 hours=112 rooms per hour \text{Rate of 1 worker} = \frac{1}{3} \times \frac{1 \text{ room}}{4 \text{ hours}} = \frac{1}{12} \text{ rooms per hour}

Step 2: Determine the equivalent rate when 4 workers are involved.
If each worker has a rate of 112 rooms per hour \frac{1}{12} \text{ rooms per hour} , then 4 workers would have a combined rate of:

Rate of 4 workers=4×112 rooms per hour=412 rooms per hour=13 rooms per hour \text{Rate of 4 workers} = 4 \times \frac{1}{12} \text{ rooms per hour} = \frac{4}{12} \text{ rooms per hour} = \frac{1}{3} \text{ rooms per hour}

Step 3: Calculate the time required for 4 workers using the combined rate.
To complete 1 room, the time required by 4 workers is:

Time=WorkRate=1 room13 rooms per hour=3 hours \text{Time} = \frac{\text{Work}}{\text{Rate}} = \frac{1 \text{ room}}{\frac{1}{3} \text{ rooms per hour}} = 3 \text{ hours}

Therefore, the solution to the problem is 3 hours.

3

Final Answer

3 hours

Key Points to Remember

Essential concepts to master this topic
  • Rule: More workers means less time for same job
  • Technique: Find rate per worker: 112 \frac{1}{12} rooms/hour ÷ 3 = individual rate
  • Check: 4 workers × 3 hours = 12 worker-hours = 3 workers × 4 hours ✓

Common Mistakes

Avoid these frequent errors
  • Adding workers and hours instead of using inverse relationship
    Don't think 3 workers + 1 worker = 4 hours - 1 hour = 3 hours by simple addition! This ignores that work rate increases with more workers. Always calculate individual worker rate first, then multiply by new number of workers.

Practice Quiz

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What is the ratio between the orange and gray parts in the drawing?

FAQ

Everything you need to know about this question

Why don't I just divide 4 hours by 4 workers to get 1 hour?

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That would give each worker only 1 hour to paint the entire room! Remember, we need to find the rate per worker first, then see how long it takes when workers combine their efforts.

How do I know this is an inverse proportion problem?

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Look for the pattern: more workers = less time for the same job. When one quantity increases and another decreases for a constant amount of work, it's inverse proportion.

What if the numbers don't work out evenly?

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That's normal! Work rate problems often give decimal answers. Just make sure to calculate the individual worker rate carefully using fractions: 1 room12 worker-hours \frac{1 \text{ room}}{12 \text{ worker-hours}} .

Can I use a shortcut formula?

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Yes! Use: Workers₁ × Time₁ = Workers₂ × Time₂. So 3 × 4 = 4 × Time₂, giving Time₂ = 3 hours. This works because total worker-hours stays constant.

What does 'worker-hours' mean?

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Worker-hours is the total amount of work needed. Think of it as: if 1 worker needs 12 hours, that's 12 worker-hours. Whether it's 3 workers for 4 hours or 4 workers for 3 hours, it's still 12 worker-hours total!

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