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An urn contains 10 pebbles numbered from 0 to 9. Three balls are drawn in succession from the urn with replacement. After each a draw a number is associated to the pebble and registered. If the numbers associated with the pebbles is for example 015 is drawn, we get 15.

(i) what is the probability of getting more than 9.

(ii) what is the probability of getting 100.

(iii) what is the probability of getting less than 100.

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    @joriki edited appropriately...2012-06-05

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Remember all values are divided by 10^3 to find out the probability. Because balls 1,2 and 3 have 0-9 possible values.

iii) is simple, 1st ball has only one possible value 0 and balls 2 and 3 have 0-9, which makes 10^2.

ii) number of ways of getting 100 is just 1.

i) number of possible entries of 1 and 2 is just 1 (00) and there are 10 possible entries for the last ball 0-9, which makes it 10 possible ways of getting a value less than or equal to 009, subtract this from 10^3 and that's your answer.

Divide all numbers by 10^3.

Please correct me if i've missed out on something.

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    I think you're right, count, but I also think it would have been better for you to include what you think, and why you think it, in your question. That would make it easier for people to see what, if anything, you don't understand, and to target answers to helping you with what you need.2012-06-05