Question 379058
If all of the letters in TEXTBOOKS were distinct, then there would be 9! = 362,880 ways to arrange the letters. However, there are two O's and two T's. To deal with this over-counting, we divide by 2 to account for the O's (since something like BOTXKOTSE is counted twice) and divide by 2 again for the T's. This leaves us 9!/4, or 90,720 distinguishable ways.