Jamie purchased a dvd that was on sale for 15% off. the sales tax in her county is 5%. let y represent the original price of the dvd. write an expression that can be used to determine the final cost of the dvd.
y − 0.15y
0.05(0.85y)
y − 0.85y + 0.05y
1.05(0.85y)

Since y is the original cost, let z represent the final cost. So, we set up the expression, (0.12y + y) - 0.03y = z. That shows first the sale, then the tax. From there, we simplify to get 1.12y - 0.03y = z, then simplify it more to get 1.09y = z. We take away the z, and get that the cost, which is 1.09, or 109%, or y (1.09y).