Question Detail

STA 112 PERMUTATIONS AND COMBINATIONS Objective Question

Question

What is the number of ways to arrange the letters of the word 'BANANA' so that no two 'N's are together?
Options
A 40
Correct Answer
B 60
C 80
D 100
Correct Answer

Option A is the correct answer.

Detailed Explanation

The word 'BANANA' has 6 letters: B, A, A, A, N, N. There are 3 A's, 2 N's, and 1 B.First, arrange the letters other than 'N's: B, A, A, A. The number of ways to arrange these 4 letters, with 3 A's identical, is 4! / 3! = 4 ways.These arrangements create 5 possible gaps where the 'N's can be placed to ensure no two 'N's are together: _ L1 _ L2 _ L3 _ L4 _We need to choose 2 of these 5 gaps for the two 'N's. Since the 'N's are identical, the order of placing them in the chosen gaps doesn't matter. This can be done in 5C2 ways.5C2 = (5 * 4) / (2 * 1) = 10 ways.Therefore, the total number of arrangements where no two 'N's are together is (Arrangements of BAAA) * (Ways to place N's) = 4 * 10 = 40 ways.

Hint

Use the gap method. Arrange the letters that are not restricted first, then place the restricted letters in the gaps created.

Question Info