Symmetric Letters

(CAT 2002)

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.

1. How many four-letter computer passwords can be formed using only the symmetric letters (no repetition allowed)?
a. 7,920
b. 330
c. 14,640
d. 4,19,430

2. How many three-letter computer passwords can be formed (no repetition allowed) with at least one symmetric letter?
a. 990
b. 2,730
c. 12,870
d. 15,600

For Answers click here.