CAT Quantitative Ability Questions | CAT Permutation, Combination and Probability questions
Comprehension
Directions for questions: Read the information given below and answer the questions that follow :
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.
CAT/2002
Question . 37
How many three-letter computer passwords can be formed (no repetition allowed) with at least one symmetric letter?
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Explanatory Answer
Method of solving this CAT Quantitative Ability Question from Permutation, Combination and Probability question
(c) Total three-letter computer passwords from any of the26 letters = 26 × 25 × 24
Again, three letter passwords from asymmetric letters= 15 × 14 × 13
∴ Passwords with atleast one symmetric letter= 26 × 25 × 24 – 15 × 14 × 13 = 12870