13.318. The price of one product was reduced twice, each time by $15 \%$. For another product, which initially had the same price as the first, the price was reduced once by $x \%$. What should the number $x$ be so that after all the specified reductions, both products have the same price again?
## Solution.

Let $z$ be the original price of the product. After the first reduction, the price became $z-0.15z=0.85z$, and after the second $0.85z-0.85 \cdot 0.15z=0.85^2z$. According to the condition, $z-\frac{x}{100}z=0.85^2z$, from which $x=(1-0.85^2) \cdot 100=27.75\%$.

Answer: $27.75\%$.