AP BIOLOGY

Detailed explanation-1: -=120 ways, with 6 spaces in between them and at the ends. Choose one of these spaces for A and another for B; makes 120⋅6⋅5=3600 in total.

Detailed explanation-2: -So total there are 24 possible arrangements.

Detailed explanation-3: -There are 60 different 3-letter combinations of A, B, C, D, E.

Detailed explanation-4: -= 4 * 3 * 2 *1 = 24 ways to arrange four letters.

Detailed explanation-5: -The number of combinations of n objects taken r at a time is determined by the following formula: C(n, r)=n! (n−r)!