Brain Teaser Of The Day: Hardware Store Purchase

Sam goes to the hardware store to buy something for his house.

He asks the price from the store owner who replies, “If you buy one it will cost you $10, and if you buy fifty it will cost you $20”.

Sam asked, “What if I buy 987?”

The owner replied, “Oh, that’ll cost you $30.”

What is Sam buying?

Brain Teaser Of The Day: Hardware Store Purchase