My memory's not what it used to be (too much internet pron, ya know? 😉 ), but the way I figured it out was like this:
Sally can paint the house in 4 hours, or do 1/4 of the house in one hour.
John can pain the house in 6 hours, or do 1/6 of the house in one hour.
Break it down to lowest common denominator:
Sally = 1/4, or 3/12 John = 1/6, or 2/12
Now add them up, and you find out how much of the house gets painted each hour, 5/12.
Then it's a simple algebra equation:
1/5=x/12, or 5x=12, or x=2.4hours it will take them to paint the house.
The simple way to check an equation like that is to figure out that in 2.4 hours, Sally will have painted 7.2/12 of the house (3/12 x 2.4), and John will have painted 4.8/12 (2/12 x 2.4), for a grand total of 7.2 + 4.8/12, or 12/12.....the entire house! 🙂
And yes, my brain often works in convoluted ways like this!! LOL
