SOLUTION: Four employees washed 20 cars and five hours how long would it take for five employees to watch the same number vehicles

Question 1127301: Four employees washed 20 cars and five hours how long would it take for five employees to watch the same number vehicles
Found 3 solutions by Boreal, greenestamps, josgarithmetic:
Answer by Boreal(15235)   (Show Source): You can put this solution on YOUR website!
Four employees took 5 hours to wash 20 cars. That is 1 hour per employee per car
5 employees for 20 cars will need 4 hours.

Answer by greenestamps(13196)   (Show Source): You can put this solution on YOUR website!

The solution by @boreal is one common way of solving problems like this; in this case you find the number of cars per person per hour from the given information and use that to answer the question.

Another common method that I personally find far easier to use is to see what factor changed from one scenario to the other and determine from that how the other factors had to change.

In this problem there are a certain number of employees washing a certain number of cars, and we want to know how long it would take a different number of employees to wash the same number of cars.

Same number of cars, with the number of employees changed by a certain factor, means the number of hours must be changed by a factor that is the reciprocal. More employees means less time by the same factor; fewer employees means more time by the same factor.

So my preferred method for solving this problem is simply this:

5/4 as many employees (5 instead of 4) means 4/5 as much time; 4/5 of 5 hours is 4 hours.
Answer by josgarithmetic(39614)   (Show Source): You can put this solution on YOUR website!
4 employees
5 hours
20 cars

5 employees
unknown hours, x
same 20 cars

The 5 employees is a faster group. This group works 1.25 times as fast as the 4-employee group.

Same factor r, for rate, on both sides.

-------four hours for the 5-employee group to wash the same 20 cars.
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