11.
12. How many gallons each of cream containing 33% butter fat and milk containing 6% butter fat must be mixed to produce 10 gallons of cream containing 25% butter fat?
13. I have $6 in dimes, quarters, and half-dollars, there being 33 coins in all. The number of dimes and quarters together is ten times the number of half-dollars. How many coins of each kind are there? (College Entrance Board.)
Reference: The last part of the chapter on Quadratic Equations in any algebra.
THE THEORY OF QUADRATIC EQUATIONS
I. To find the sum and the product of the roots.