Question 183490

Let x=amount of 15% solution needed
Now we know that the amount of pure stuff in the 15% solution (0.15x) plus the amount of pure stuff in the 20% solution (0.20*4) has to equal the amount of pure stuff in the final mixture (0.17(4+x)). So:

0.15x+0.20*4=0.17(4+x) get rid of parens
0.15x+0.80=0.68+0.17x subtract 0.68 and also 0.15x from each side
0.15x-0.15x+0.80-0.68=0.68-0.68+0.17x-0.15x collect like terms
0.12=0.02x  divide each side by 0.02
x=6 oz----------------------amont of 15% solution needed

CK
0.15*6+0.20*4=0.17*10
0.90+0.80=1.70
1.70=1.70

Hope this helps---ptaylor