The class treasury contained 30$ in nickels and dimes. If there were 500 coins than how many coins of each type are there?

Equation 1. N+D=500

equation 2 5N+10D=3000

This is for equation 1

N=500-d

Substitute into equations 2 and solve for D

5N+10D=3000

5 (500-D) + 10D=3000

2500-5D+10D=3000

5D=500

D=100

Lets go back the equation 1

N=500-D

N=500-100

N=400

there are 400 Nickles and 100 Dimes