Question

can you help me get the formula to solve this.
A newspaper sales stand has 200 coins at the end of a day, all dimes and quarters. If the value of the coin is $42.50, how many of each denomination coin were in the stand?

Answer 1

Let x = # of dimes , y =# of quarters

x+y = 200
.10x + .25y = 42.50

Answer 2

can you tell me why its .10 and .25

Answer 3

i came up with my own solution, to my understanding. is it right?
2x + 42.50 = 200
2x = 200-42.50
2x = 157.5
x = 78. 75

i checked it,
2(78.75) + 42.50 = 200
157.5 + 42 .50 = 200
200 = 200