- #1

smckech

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1. What is the probability of picking three distinct numbers (order does not matter)? (digits 0-9, ex: 123)

2. What is the probability of picking any three numbers in any order (order does not matter)? (digits 0-9, examples: 111,112,123)

3. What is the probability of picking two of the same numbers in any order (order does not matter)? (digits 0-9, examples 112,221,332)

My thoughts so far:

Question 1: I was thinking 10 c 3 and so it would be 120.

Question 2: The 'ask a scientist' website states that the answer is 120/1000. I disagree, I think it should be 220/1000 (a numerator greater than 120 at least, I may have got the 220 figure wrong).

My reasoning: Any three numbers could be three distinct, two of the same or all the same. Three distinct would be the 120, two of the same I think would be 90 and all the same would be 10. Giving a 220 total.

Question 3: This question is a part of question 2. I think it is 90 based on that fact that for each case of two numbers the same (10) there are 9 possibilities in each for the third number and so 9x10 = 90 possible ways of choosing two numbers the same.