Question

You obtain 10 ml of a 21% peroxide solution from a mixture of a 15% solution and a 30% solution. How much of the 15% solution is used in the mixture?

Answer 1

solve
\[.15x+.30(10-x)=2.1\]

Answer 2

put x = ml of 15% solution, it will contribute
\[.15x\] since the total is 10 the amount of 30% solution will be
\[10-x\] and it will contribute
\[.30(10-x)\]
for a total of
\[.15x+.30(10-x)\]
you want the total to be 21% of 10 =2.1 so set them equal and solve
\[.15x+.30(10-x)=2.1\]

Answer 3

Thank you! I got almost that far but was trying to use .30(y) instead of .30(10-x).