Sally has $1.50 worth of change in her pocket - - all nickels and dimes. She has three times as many nickels as dimes. Find the number of each

If we use x for the number of dimes, and y for the number of nickels, then from this problem we know:

x (.10) + y (.05) = 1.50

since each dime we have is another. 10 dollars, and each nickel is another. 05 dollars, as well as

3x=y

since we have 3 times as many nickels, we have to multiply dimes by 3 to have the same number of coins.

plugging this in to the first equation we get:

x (.10) + 3x (.05) = 1.50

.1x+.15x=1.5

.25x=1.5

x=6

Sally has 6 dimes.

Plugging this back in to 3x=y, we get

3 (6) = y

18=y

So, Sally has 18 nickels