Find the number of ways of arranging letters of HAVANA so that V and N do not appear together.
HAVANA = 6 letters =6! =720 permutations. But, because letter "A" is repeated 3 times, then we have:
720 / 3! =120 permutations. 120 /6 = 20 times that each letter appears somewhere in the 120 permutations.
And in 2 instances, the 2 letters "N" and "V" will be next to each other. Or: 2 x 20 = 40 times when they will be together. So: 120 - 40 =80 instances when they will NOT be together.