Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:
find those permutations that have no letters between I and subtract it from the total permutation.
1. total permutation: 7!
2. permutations to subtract from 1, just treat two I's as one element. it is 6!. tricky here: since I am going to subtract it from 7!, i need to consider the permutations of 2 I's together. so this intermediate result is 2*6!.
3. 7! - 2*6! is the rest of the permutations. but there are 2 T's, so the order does not matter for T. then divide 7!-2*6! by 2.