When a die is rolled three times,
1. what is the probability of three no.s being all different?
2. And is the opposite of that event two or three no's being the same?
1. You are concerned with not matching the first toss, no matter what it is and not matching the second toss either (5/6*4/6).
2. Again the first toss can be any number. For two the same, you need one the same and one different (1/6*5/6). From that, you should be able to determine the probability of 3 the same. (Either-or probabilities are determined by adding the separate probabilities.)
I hope this helps.