You have $2.75 in dimes and quarters, and you have a total of 17 dimes and quarters. How many of each type of coin do you have?

Answer 1

D+Q=17
or Q=17-D

and 10D+25Q=275
or 10D+25(17-D)=275
solve for D, then solve for Q

Answer 2

Distribute 25
10D+425-25D=275
Add like variables
425-15D=275
Subtract 425
-15D=-150
Divide Each Side by -15
D=10
Plug D into equation to solve for Q.
Q=17-10
Q=7