Drawing 4 balls from an urn without replacement and a bonus ball

Rzarekta

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May 17, 2017
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An urn contains 9 white, 9 red, 9 blue and 9 green balls. 4 balls are drawn randomly without replacement and a fifth bonus ball is drawn from the same urn.
a) What is the probability of drawing 3 red balls and a non-red bonus ball?
b) What is the probability of drawing 2 black balls and 1 black bonus ball?
I managed to use a general formula for drawing 5 balls but I cannot modify it for the required solution. Please refer to the attached images for my progress.

Lucky 5.JPG

Lucky 5-1.JPG
 
An urn contains 9 white, 9 red, 9 blue and 9 green balls. 4 balls are drawn randomly without replacement and a fifth bonus ball is drawn from the same urn.
a) What is the probability of drawing 3 red balls and a non-red bonus ball?
b) What is the probability of drawing 2 black balls and 1 black bonus ball?
I managed to use a general formula for drawing 5 balls but I cannot modify it for the required solution. Please refer to the attached images for my progress.

View attachment 8218

View attachment 8219
Hi. What have you tried? Can you please show us what you tried? We can't HELP you, if we do not know where you are stuck.
Hint: You are drawing 5 balls with some information about the 5th ball.
 
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