Lesson: Challenging Problem Solving - 24

Tough Rate Questions

If five machines working at the same rate can do of a job in 30 minutes, how many minutes would it take two machines working at the same rate to do of the job?

In our example, we are asked to use the rate of five machines to find out the rate of two machines. Once we determine this rate, we can then figure out how much time is needed for two machines to complete part of the job.

On the surface, this is a tricky question. But what makes it tricky? The change in the number of machines complicates this problem. How are we to work with two rates that are based on different numbers of machines and different parts of the job?

The answer: use logic and quick calculation to find the correct answer. In this question, the new number of machines is a proportion of the old number of machines. By recognizing and working with this key relationship, we will be able to get to the correct answer quite easily.

Let's see how this works.

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