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Two balls are drawn in succession out of a box containing 2 red and 5 white balls. Find the probability that at least one ball was red , given that the first ball​ was:

​(A)  replaced before the second draw.
​(B)  not replaced before the second draw.

User Teofil
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1 Answer

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A) (2/7 x 2/7) + (2/7 x 5/7) + (5/7 x 2/7) =

4/49 + 10/49 + 10/49 = 24/49 <== this is the answer

B) (2/7 x 1/6) + (2/7 x 5/6) + (5/7 x 2/6) -

2/42 + 10/42 + 10/42 = 22/42 <== this is the answer

The second answer could be simplified to 11/21 (only write this answer if it wants the simplified version, otherwise write the one above)

Hope This Helps You!

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User Stefan Negele
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