Question

A boy has $1.35 in his bank in nickels and dimes. There are 9 more nickels than dimes. How many types of each coin are there?

Answer 1

let n = # of nickels
let d = # of dimes
It follows then,
1.35 = 0.05n +0.10d
d+9 = n

Answer 2

Do you get that?

Answer 3

From these two equations:
1.35 = 0.05n +0.10d
d+9 = n

We can then say that

1.35 = 0.05(d+9) +0.10d