Homework Help: geometry

Posted by please help me out!!! please on Monday, February 11, 2013 at 10:39am.

In the English alphabet, there are 7 capital letters that look the same after being rotated 180∘. Those letters are H, I, N, O, S, X, and Z. How many different 3 letter "words" can be made from these letters such that when the word is rotated 180∘, the resulting word is the same?

geometry - Reiny, Monday, February 11, 2013 at 10:51am
Clearly the 1st and 3rd letter must be the same, but the middle can be any of the 7 letters

number of ways = 7 x 7 x 1 = 49

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