An all day parking meter only takes dimes and quarters. If it contains 100 Coins with a total value of $14.50, how many of each type of coin are in the meter?

X = # of dimes, y = # of quarters

100 = x+y

14.50 =.10x+.25y

This is substitution.

100 = x+y

x = 100-y

14.50 =.10 (100-y) +.25y

14.50 = 10-.10y +.25y

4.50 =.15y

30 = y, OR there are 30 quarters

100=x+y >>> 100=x+30 >>> 70=x, OR there are 70 dimes