Prime Gum (3/16)

(Someone asked for a math problem. Hope this does the trick.)

In grade school, a friend of mine sold sticks of gum for profit. One day, I had 50 cents in my pocket and decided to buy one. After popping the gum in my mouth, I realized that the price of the gum and the change I had leftover were both prime numbers. Then I bought two more sticks of gum, and my change was still a prime number. Unfortunately, I didn't have enough money to buy another stick.

How much was a stick of gum?


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