Question 74733
Let x=the number of gal of 9% plant food
Then 10-x=the number of gal of 25% plant food

Now we know the amount of pure nitrogen before the mixture takes place must equal the amount of pure nitrogen after the mixture takes place.  So our equation to solve is:

0.09x+0.25(10-x)=0.15(10)  get rid of parens

0.09x+2.5-0.25x=1.5  subtract 2.5 from both sides

0.09x+2.5-2.5-0.25x=1.5-2.5  collect like terms

-0.16x=-1  divide both sides by -0.16

x=6.25 gal ---------------of the 9% plant food must be combined

ck

0.09(6.25)+0.25(3.75)=0.15(10)
0.5625+0.9375=1.5
1.5=1.5


Hope this helps---ptaylor