SOLUTION: Joe can wash all his cars twice as fast as his soon. If they work together, the wash all the cars in 2hrs. How long will it take his son to wash all the cars?

Algebra ->  Rate-of-work-word-problems -> SOLUTION: Joe can wash all his cars twice as fast as his soon. If they work together, the wash all the cars in 2hrs. How long will it take his son to wash all the cars?       Log On


   

Question 955291: Joe can wash all his cars twice as fast as his soon. If they work together, the wash all the cars in 2hrs. How long will it take his son to wash all the cars?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +1%2Ft+ ( all the cars ) / hr = Joe's rate
+1%2F%282t%29+ = his son's rate ( all the cars ) / hr
+1%2F2+ = rate working together ( all the cars ) / hr
--------------------
Note that ( all the cars ) can be considered 1 job
which is the 1 in the numerator
Add their rates to get rate working together
+1%2Ft+%2B+1%2F%282t%29+=+1%2F2+
Multiply both sides by +2t+
+2+%2B+1+=+t+
+t+=+3+
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His son's rate is:
+1%2F%282t%29+=+1%2F%282%2A3%29+
+1%2F%282t%29+=+1%2F6+ ( all the cars )/hr
It takes his son 6 hrs to wash all the cars