Answer:13 dimes and 7 quarters.
Explanation:
dimes and quarters are 10 cents and 25 cents, so its 0.1 and .25. There are 20 coins so x(dimes)+y(quarters=20. The added cost is 3.05. .1x+.25y=3.05. This is a system of equations. We can multiply the first one by -.1 to cancel x. -.1x-.1y=2 and .1x+.25y=3.05. Next, .15y=1.05 and this divides out and y=7. We have 20 coins in total so 20-7=13. There are 13 dimes and 7 quarters.