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A box contains 5 white balls and 6 black balls. Two balls are drawn out of the box at random. What is the probability that they both are white?

 May 27, 2019
 #1
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5 + 6 means there are 11 balls in total.

 

Of these 11, 5 are white, so the probability of the first ball that's drawn being white is 5/11.

 

I'll assume the ball isn't put back into the box. So now you have 10 balls left, 4 of which are white.

('cause you already removed one white ball, the total number of balls and the number of white balls goes down)

Which means that the second pull has a 4/10 chance of being a white ball.

 

Both of these events need to happen, so you multiply the chances:

 

(5/11) * (4/10) = 2/11

 May 27, 2019
 #2
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Thank you, I understand fully now. 

Ahemm, mods, pls lock now.

Guest May 27, 2019
edited by Guest  May 27, 2019

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