A collection of dimes and quarters is worth $6.50. There are 35 coins in all. How many dimes are there?

The answer to your problem is 15 if you need work here it is

x=Quarters y=Dimes

so the total number of coins is 35 the other equation is

.25x+.1y = 6.5

Now we can solve for x and y easily

y=35-x

We can substitute the into the other equation

.25x+.1 (35-x) = 6.5

Lets Simplify it

.15x=3.5=6.5

.15x=3

x=20

Now we can sub stitute x=20 back into the first equation to get y and if we get x+y=35 then 20+y=35 we know that there are 15 dimes left over so 20+15=35

15 dimes

20 quarters=5$ + 15 dimes = 1.50 which = 6.50 and 35 coins