$\underline{\text { Sabin A. }}$.

Ofenya bought a batch of pens at a wholesale market and offers customers either one pen for 5 rubles or three pens for 10 rubles. From each customer, Ofenya makes the same profit. What is the wholesale price of a pen?
According to the condition, the difference $10-5=5$ is the wholesale price of two pens.

## Answer

2 rubles 50 kopecks.