Question 1017457
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if it takes 3 people 8 hours to wash 15 cars, how long would it take 2 people to wash 7 1/2 cars?
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<pre>
The rate of work calculated based on the first part of the condition, is

{{{15/(3*8)}}} car-per-person-per-hour.

Let t be the time under the question. The the rate of work calculated based on this (second) part of the problem is 

{{{7}}}{{{1/2}}} : (2*t) = {{{15/(2*2*t)}}}.

We assume that the rate of work remains the same. It gives us an equation

{{{15/(3*8)}}} = {{{15/(2*2*t)}}}.

First reduce what you can:

{{{1/(3*2)}}} = {{{1/t}}}.

Now solve this proportion for t:

t = 3*2 = 6.

<U>Answer</U>. It will take 6 hours.
</pre>

If you want to see more solved rate of work problems, look into the lesson <A HREF=http://www.algebra.com/algebra/homework/Rate-of-work-word-problems/Rate-of-work-problem.lesson>Rate of work problems</A> in this site. 


At the end of that lesson you will find the list of other types rate of work problems that might be interesting to you, too.