SOLUTION: If george washed a car in 20 minutes and sally washed the same car in 15 minutes how long would it take them to wash the car together?

Algebra ->  Rate-of-work-word-problems -> SOLUTION: If george washed a car in 20 minutes and sally washed the same car in 15 minutes how long would it take them to wash the car together?      Log On


   

Question 973876: If george washed a car in 20 minutes and sally washed the same car in 15 minutes how long would it take them to wash the car together?
Found 2 solutions by josmiceli, 428225:
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Add their rates of washing to get
their rate washing together
George's rate:
[ 1 car ] / [ 20 min ]
Sally's rate:
[ 1 car ] / [ 15 min ]
------------------
Let +t+ = time in minutes working together
+1%2F20+%2B+1%2F30+=+1%2Ft+
Multiply both sides by +60t+
+3t+%2B+2t+=+60+
+5t+=+60+
+t+=+12+ min
It takes them 12 min working together

Answer by 428225(90) About Me  (Show Source):
You can put this solution on YOUR website!
The working out should be:
1%2F15%2B1%2F20=1%2Ft
7%2F60=1%2Ft
Therefore
t=60%2F7
t=8.57 minutes