Answer: 45.
- A 10
- B 45
- C 90
- D 100
Correct answer: B. 45
Explanation: Each handshake = 1 unique pair of people. Count pairs from 10: C(10,2) = 10×9/2 = 45. Order within a pair doesn't matter, so no doubling.
Counting tree for selecting 2 items from {A, B, C} without repetition: 3 x 2 = 6 ordered arrangements.
Concept context
Counting, arrangements, and selections