How many different 6-letter strings are made up of 2 a's, 2 b's and 2 c's?

The answer to this question would be:90 different words/strings.

This is a question about probability. In this question, there are 3 different kinds of the letter that consist of 2 letter each. The same letter will be considered same, so the probability will lessen if there are more same letter. The calculation would look like this : 6! / (2! 2! 2!) = 90 different words/strings.