Answer: 2 n.
- A 2<sup>n</sup>
- B n!
- C n²
- D 2<sup>n-1</sup>
Correct answer: A. 2<sup>n</sup>
Explanation: Set x=y=1: (1+1)<sup>n</sup> = 2<sup>n.</sup> Sum of all binomial coefficients = 2<sup>n.</sup>
Counting tree for selecting 2 items from {A, B, C} without repetition: 3 x 2 = 6 ordered arrangements.
Concept context
Counting, arrangements, and selections