The original price was multiplied by a certain percentage, say x/100, and it became the discounted price. So, we have
[tex] 28 \cdot \frac{x}{100} = 22.95 [/tex]
Solving for x, we have
[tex] x = \frac{22.95\cdot 100}{28} = \frac{2295}{28} \approx 82 [/tex]
So, the discounted price is approximately the 82% of the original price. This means that 18% of the original price was discounted.