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Joint Entrance Examination
Mathematics
Probability
Question 260
Question 260 of 417
Medium
MCQ
An urn has 2 balls, each white or black. A white ball is added, then a ball drawn at random. Find the probability it is white.
A
1
/
4
1/4
1/4
B
2
/
3
2/3
2/3
C
1
/
5
1/5
1/5
D
1
/
3
1/3
1/3
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Official solution
With the possible initial compositions equally weighted, adding a white ball and drawing: \[P(\text{white}) = \frac{2}{3}\]
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