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A box contains 4 white balls and 5 red balls. I draw 3 of them out of the box, one at a time, and set them aside. What is the probability that the balls I draw alternate between the two colors?

 Jun 10, 2018
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We have two  scenarios

 

White, Red, White   =  4/9 * 5/8 * 3/7  = 60/504    ....and...

Red, White, Red  =  5/9 * 4/8 * 4/7  =  80 / 504

 

Adding the  probabilities  we  have  [ 60 + 80 ] / 504  = 140/504  =  5/18

 

 

cool cool cool

 Jun 10, 2018

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