How many three-letter code symbols can be formed from the letters A, C, K, L , and M without repetition?

Answer 1

Noting that ACK is not the same as KAC,

You can choose from 5 letters for your first

Then you can choose from 4 letters for your second.

Finally you can choose from 3 letters for your first

So you can choose in 5 * 4 * 3 ways.