SOLUTION: If Susie can paint a house in 4 hrs and David can paint a house in 6 hrs. How long will it take them to paint it together? One answer that was given was 2hr and 24 min, but I'm no

Algebra ->  Rate-of-work-word-problems -> SOLUTION: If Susie can paint a house in 4 hrs and David can paint a house in 6 hrs. How long will it take them to paint it together? One answer that was given was 2hr and 24 min, but I'm no      Log On


   

Question 74314: If Susie can paint a house in 4 hrs and David can paint a house in 6 hrs. How long will it take them to paint it together? One answer that was given was 2hr and 24 min, but I'm not sure how they got it.
Answer by funmath(2933) About Me  (Show Source):
You can put this solution on YOUR website!
If Susie can paint a house in 4 hrs and David can paint a house in 6 hrs. How long will it take them to paint it together?
This is the way I was taught this, but I know there is another way to do this:
Susie can paint 1 house in 4 hrs, her work rate is:1/4
David caan paint 1 house in 6 hrs, his work rate is: 1/6
They both can paint 1 house in x hrs, their combined work rate is:1/x
:
Problem to solve:
1%2F4%2B1%2F6=1%2Fx
%283%2F3%29%281%2F4%29%2B%282%2F2%29%281%2F6%29=1%2Fx
3%2F12%2B2%2F12=1%2Fx
5%2F12=1%2Fx Cross multiply, or flip both sides over and you have:
5x=12
5x%2F5=12%2F5
x=12%2F5
x=12/5 hrs.
x=2 and 2/5 hrs there are 60 minutes in an hour
x=2 hrs and (2/5)(60)min
x=2 hrs and 24 mins.
Happy Calculating!!!!