Question 921002
Let's think of it this way... 

What is the value of a dime? ... .10
What is the value of a nickel ... .05
Let n = nickels
d = dimes
.05n + .10d= 1.20 multiply by 100
5n + 10d = 120

Also they said the amount of dimes and nickels are equal 
n=d

substitute n = d into the other equation,

5d + 10d = 120 
15d =120

d = 8  so n = 8

Lets check it.
5*8 + 10*8 = 120 
40  + 80 = 120
120 = 120