Question was
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?
Explanatory Answer
There are three possible cases that will satisfy the condition of forming three letter passwords with at least 1 symmetric letter.
Case 1: 1 symmetric and 2 asymmetric or
Case 2: 2 symmetric and 1 asymmetric or
Case 3: all 3 symmetric
= {(11C1 * 15C2) + (11C2 * 15C1) + 11C3} * 3!
= {11 *
+ 
* 15 + 
} x 6
= {1155 + 825 + 165} * 6
= 2145 * 6 = 12870
i hope you liked that
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?
Explanatory Answer
There are three possible cases that will satisfy the condition of forming three letter passwords with at least 1 symmetric letter.
Case 1: 1 symmetric and 2 asymmetric or
Case 2: 2 symmetric and 1 asymmetric or
Case 3: all 3 symmetric
= {(11C1 * 15C2) + (11C2 * 15C1) + 11C3} * 3!
= {11 *
+ * 15 + } x 6= {1155 + 825 + 165} * 6
= 2145 * 6 = 12870
i hope you liked that
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