Question 152465
Let x=amount of 9% solution needed

Now we know that the amount of pure cleaning solution in the 9% mixture (0.09x) plus the amount of pure cleaning solution in the 13% mixture (0.13*10) has to equal the amount of pure cleaning solution in the final mixture (0.11(10+x)).  So our equation to solve is:

0.09x+0.13*10=0.11(10+x)  get rid of parens and simplify

0.09x+1.3=1.1+0.11x  subtract 1.1 and also 0.09x from each side

0.09x-0.09x+1.3-1.1=1.1-1.1+0.11x-0.09x  collect like terms

0.2=0.02x  divide each side by 0.02
x=10 pints----------------------------------amount of 9% solution needed

CK

0.09*10+0.13*10=0.11*20
0.9+1.3=2.2
2.2=2.2


Hope this helps---ptaylor