motor's oil is 1-to-15 mix of oil to gas; find liters in 20L

[rick]

How do I solve this word problem? One type of motor requires a mixture of oil and gasoline in a ratio of 1 to 15 (that is, 1 part of oil to 15 parts of gasoline). How many liters of each are contained in a 20-liter mixture?

[artichoke]

x = amount of oil
y = amount of gasoline

x+y = 20
x/y = 1/15

solve, e.g.

second equation is x = y/15.

then first equation is y/15 + y = 20

solve for y then x.