Question

Mike bought 16 paperback books at the used book store for $10.95. Some cost $0.60 and some cost $0.75. How many of each did he buy?

Answer 1

x=number of books that cost 0.60
y=number of books that cost 0.75

x+y=16
0.6x+0.75y=10.95

solve
multiply second equation by 10 for nicity
6x+7.5y=109.5

multiply first equesiotn by -6 and add to second

-6x-6y=-96
6x+7.5y=109.5 +
0x+1.5y=13.5

1.5y=13.5
divide both sides by 1.5
y=9

sub back
x+y=16
x+9=16
minus 6
x=7

seven 0.60 books and nine 0.75 books