Question 1024478
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There are 8 blue balls, 8 yellow balls and 8 red balls of the same type inside a sack. How many balls must be pulled out to ensure that we get a pair of yellow balls?
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8 + 8 + 2 = 18 balls.


In the worst case you will pull out 8 blue balls and 8 red balls before first yellow ball will arise. 


But after that you will pull out only yellow balls, in reward!