SOLUTION: i want some very difficult questions in permutations and Combinations with the solutions and explanations >>> please

Question 388015: i want some very difficult questions in permutations and Combinations with the solutions and explanations >>> please
Answer by mdenny(8) (Show Source): You can put this solution on YOUR website!
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 symmteric 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 = 1287O
RELATED QUESTIONS
how to know that the permutations and combinations in... (answered by Fombitz,ikleyn)

The number of squares that can be formed on a chess board is-: a)204 b)304 c)1296... (answered by KMST)

I have a test in lagarithm after two weeks can you please give me some difficult... (answered by Alan3354)

There are 25 questions on a test with four multiple choice answers each. How many total... (answered by stanbon)

How many unique ways are there to arrange the letters in the word ERROR? Deals with... (answered by ikleyn)

Sam had 9 sweaters. If he wore one a day for a week, how many permutations are possible? (answered by edjones)

I'm totally lost with the probability and statistics, I have 2 discussions questions and... (answered by stanbon)

A dance instructor asks each student to do 4 out of the 10 dance routines. Of the 10... (answered by CPhill)

in our class for algebra 2 we are working on probablity and also permutations and... (answered by stanbon)