Question 400609
Let x=number of lbs of nut mixture used
Now we know that the amount of pistachios that we have before the mixture takes place has to equal the amount of pistachios that we have after the mixture takes place.
Amount of Pistachios before the mixture takes place:  5+0.70x
Amount of pistachios after the mixture takes place: 0.80(5+x)
So, our equation to solve is:
5+0.70x=0.80(5+x) get rid of parens and simplify
5+0.70x=4+0.80x  subtract 5 and also 0.80x from each side
-0.10x=-1
x=10 lbs------amount of nut mixture needed

CK
5+0.70*10=0.80*15
5+7=12
12=12

Hope this helps---ptaylor