Only 2: CD and DC.
There are 720 possible permutations.
Since there are no duplicate letters in the word RAINBOW, the number of permutations of those letters is simply the number of permutations of 7 things taken 7 at a time, i.e. 7 factorial, which is 5040.
If you mean permutations of the letters in the word "obfuscation", the answer is 1,814,400.
39916800 permutations are possible for the word INFORMATION.
There are 24.
Normally, there would be 5!=120 different permutations* of five letters. Since two of the letters are the same, we can each of these permutations will be duplicated once (with the matching letters switched). So there are only half as many, or 60 permutations.* (the correct terminology is "permutation". "combination" means something else.)
There are 9,979,200
120 if A is treated the same as a. 360 if A is considered different to a.
The number of permutations of the letters SWIMMING is 8 factorial or 40,320. The number of distinct permutations, however, due to the duplication of the letters I and M is a factor of 4 less than that, or 10,080.
There are 7893600 permutations.
There are 7 factorial, or 5040 permutations of the letters in the word NUMBERS.
UNITED = 6 letters The letters in the word UNITED did not repeat so the number of permutations = 6! = 6x5x4x3x2 =720
If they are all different, then 40320.
The number of permutations of the letters in the word LOUISIANA is 9 factorial or 362,880. However, since the letters I and A are each repeated once, you need to divide that by 4 to determine the number of distinct permutations, giving you 90,720.