Question

Write the number of arrangements of the letters of the word BANANA in which two N's come together.

Answer 1

The word BANANA consists of 6 letters including three As and two Ns.
Considering both Ns together or as a single letter, we are left with 5 letters including three As.
∴ Number of arrangements of 5 things in which 3 are similar to one kind = $\frac{5!}{3!}$ = 20