Let n be the number of nickels and let d be the number of dimes.
We know that there are 30 nickels and dimes.
n + d = 30
We also know that there are 12 more nickels than dimes
d + 12 = n
Substitute this into n+d = 30
(d + 12) + d = 30
2d + 12 = 30
Subtract both sides by 12
2d = 18
Divide both sides by 2
d = 9
Mariko has 9 dimes.
Have an awesome day! :)
