You went shopping for back to school and bought packs of pens and pencils. A pack of pencils cost $2.50 and a pack of pens cost $3. You spent a total of $35 and bought a
total of 13 packs. How many packs of pencils and how many packs of pens did you
buy?

Achemist has 200 ml of a 10% sucrose solution. she adds x ml of a 40% sucrose solution. the percent concentration, y, of the final mixture is given by the rational function: the chemist needs the concentration of the final mixture to be 30%. how many milliliters of the 40% solution should she add to the 10% solution to get this concentration?