Question 22542
Let x = the percentage of antifreeze in the 16 qts of coolant after the addition of the 8 qts of 90% solution.  You can write the following equation after changing the percentages to their equvalent decimal values:

{{{8(0.15) + 8(0.9) = 16(x)}}} Simplify and solve for x.
{{{8(1.05) = 16x}}} Divide both sides by 16.
{{{0.5(1.05) = x}}}
{{{x = 0.525}}} Now change the decimal to a percent.
{{{0.525 = 52.5}}}% 
The final solution will be 52.5% antifreeze.