Hannah has only nickels and dimes in her wallet. she has a total of $2.50 and a total of 30 coins how many nickels does she have using system of equations?

Our school doesn't follow system of equations, rather a divisive pattern system. From that: 
30/2 = 15
15(10)+15(5) = 1.50 + .75 = 2.25
2.25=/=2.50

20(10)+10(5) = 2.00 + .50 = 2.50
2.50 = 2.50

She has 10 nickels.

So relativelydivide by half and start the input/output from there, continuing to adjust to find the answer you're looking for.