STATISTICS

1. Mr. Ding walks into a dollar store (Everything is $1, $2 or $3. Yes, dollar store was "everything for a dollar" before, but due to inflations, they have to rise the price of certain items.) with 100 dollars in his pocket. He leaves the store with 15 items in his bag. Then how many different combina- tions in the sense of price, e.g. four of $1, six of $2. and five of $3.) could Mr. Ding have when he left the store