If you pay $22.90 for a DVD that includes a 7% sales tax, what is the price of the DVD before the sales tax?
If y represents the price of the DVD before the tax, then the price with tax would be y + 0.07y = $22.90. Therefore 1.07 y = 22.90, or y = 22.9 ÷ 1.07 = 21.4. Be careful not to just take 7% of $22.90 and subtract. That is incorrect.