Question

A bag contains 6 red balls and 3 blue balls. 4 balls are selected at random. find the probability of selecting 4 red balls.

Answer 1

Assuming that the balls are not replaced; 

$\frac{6}{9}* \frac{5}{8}* \frac{4}{7}* \frac{3}{6}$= 5/42 

(the numbers are decreasing in the denominator as you are presumably taking out the red balls. In the denominator, there is one less ball each time since you took out a red one). 

Therefore, the probability of selected 4 red balls consecutively without replacement is 5/42. 

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