Question 110491
Let x=amount of time it takes Nancy to paint a house
Then 2x= amount of time it takes Terry to paint a house

Now Nancy can paint at the rate of 1/x houses per day
Terry can paint at the rate of 1/2x houses per day

Together they can paint at the rate of 1/7 house per day.  So our equation to solve is:

(1/x)+(1/2x)=1/7   multiply each term by 14x

14+7=2x collect like terms
21=2x  divide both sides by 2

x=10.5 days-------Amount of time it takes Nancy to paint a house

2x=2*10.5=21 days----Amount of time it takes Terry to paint a house 

CK

(1/10.5)+1/21=1/7  multiply each term by 21

2+1=3
3=3

Also

10.5*2=21
21=21


Hope this helps-----ptaylor