Question

a collection of quarters and nickels is worth 13.50. there are 78 coins in all. find the number of each coin

Answer 1

q+n=78
25q+5n=1350
divide 2nd equation by 5
5q+n=270

q+n=78
5q+n=270
mulitply first equaton by -1 and add to 2nd

-q-n=-78
5q+n=270 +
4q+0n=192

4q=192
divide both sides by 4
q=48

sub back

q+n=78
48+n=78
minus 48 both sides
n=30

30 nickles
48 quarters