Groups of three.

From the set of letters $\{A, B, C, D, E, F, G, H, I, J\}$ , how many discrete triplets can be formed?

Try solving without using combinatorics equations.

Clarifications:

• A triplet is defined to be a group of three letters, for example, $(A, B, C)$ or $(A, C, E).$
• Triplets are discrete when they contain at least one different letter. Triplets such as $(A, B, C)$ and $(A, C, B)$ are not discrete because they contain the same letters but in a different order. Triplets such as $(A, B, C)$ and $(A, B, E)$ , however, are discrete as they contain one different letter.