Pnc!!
Each of the 11 letters A, H, I, M, O, T, U, V, W, X and Z appears same when looked at in a mirror. They are called symmetric letters. Other letters in the alphabet are asymmetric letters. How many three letter computer passwords can be formed (no repetition allowed) with at least one symmetric letter?
The answer is 12870.
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1 solution
There are 2 6 ⋅ 2 5 ⋅ 2 4 possible three distinct letters password with all leters. We must subtract all passwords with three asymmetric letters i.e. we must subtract 1 5 ⋅ 1 4 ⋅ 1 3 and we are getting 12870