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How many different 10 letter words (real or imaginary) can be formed from the following letters? D, L, T, A, Q, D, L, S, Q, U
Since there are 10 letters so, assuming we cannot reuse a letter, the number of words is the number of ways we can arrange the 10 letters. There are 10 choices for the first letter. For each of these we have 9 choices for the second letter, and so on.
So the total number of choices for all the positions we have 10*9*8*7*6*5*4*3*2*1 = 10!