A collection of quarters and dimes is worth $12.40. There are 67 coins in all.
How many of each coin are there?
quarters____
dimes____

Let:x= quartersy= dimesx+y=67and.25x+.10y=12.40x=67-y.25(67-y)+.10y=12.4016.75-.25y+10y=12.4016.75-.15y=12.40Lets rearrange this:-.15y+16.75=12.40        -16.75    -16.75-.15y=-4.35the negatives cancel out.15y=4.35.15     .15y=29Back to the original x=67-yx=67-29x=38So,x=38y=29