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?  
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:
{{{1/4+1/6=1/x}}}  
{{{(3/3)(1/4)+(2/2)(1/6)=1/x}}}
{{{3/12+2/12=1/x}}}
{{{5/12=1/x}}}  Cross multiply, or flip both sides over and you have:
{{{5x=12}}}
{{{5x/5=12/5}}}
{{{x=12/5}}}
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!!!!