135: including 15 with two Os which are assumed to be indistinguishable.
If one of the Os is upper case and the other lower (so that Oct is different from oct), then the answer is 8*7*6 = 336.
There are 5P3 = 5!/2! = 5*4*3 = 60 permutations.
Permutations of 10 letters taken 3 a time = 10 x 9 x 8 = 720
September has 9 letter, of which one appears 3 times. So the number of distinct permutations is 9!/3! = 120,960
because permutations are order specific, and because there are two d's "dad" counts as only one. so it is 6 (3P3)/2 (there are two d's) so the answer is 3 DAD ADD DDA
How many four-letter permutations can be formed from the letters in the word DECAGON?
There are 195 3-letter permutations.
There are 5*4*3 = 60 permutations.
4! 4 * 3 * 2 * 1 = 24
There are 5P3 = 5!/2! = 5*4*3 = 60 permutations.
The first letter of the perm can be any of the 4, the second any of the remaining 3, the third either of the remaining 2. There are thus 4 x 3 x 2 ie 24 permutations.
Permutations of 10 letters taken 3 a time = 10 x 9 x 8 = 720
4! Four factorial. 4 * 3 * 2 = 24 permutations ------------------------
How many permutations of 3 different digits are there, chosen from the ten digits 0 to 9 inclusive?
The number of permutations of the letters MASS where S needs to be the first letter is the same as the number of permutations of the letters MAS, which is 3 factorial, or 6. SMAS SMSA SAMS SASM SSMA SSAM
We know there are 10! (ten factorial) permutations (that's about 3,628,800 permutations); however, we know that number includes repeated permutations, as there are 3 s', 3 t's and 2 i's. So we have to divide by the number of ways these can be written as individual permutations (if they were considered as unique elements), which are 3! (= 6), 3! and 2! (= 2) respectively. So our final calculation would be 3628800 / (6 * 6 * 2) = 50400 unique permutations.
A - Z means you can use the whole alphabet, which usually contains 26 letters. So a one-letter code would give you 26 permutations. 2 letters will give you 26 x 26 permutations. A three letter code, finally, will give you 26 x 26 x 26 , provided you don't have any restrictions given, like avoiding codes formed from 3 similar letters and such.
There are 4*3*2*1 = 24 of them.