GATE ME 2021 Set 2 — Question 7
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Engineering Mathematics → Probability → Conditional Probability
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Question
A box contains 15 blue balls and 45 black balls. If 2 balls are selected randomly, without replacement, the probability of an outcome in which the first selected is a blue ball and the second selected is a black ball, is ________
Correct answer
(B) (45)/(236)
Solution
Total number of balls = .
Probability of selecting a blue ball first, .
Since the selection is without replacement, the total number of balls remaining is 59.
Probability of selecting a black ball second, given the first was blue, .
The probability of the outcome (Blue first, Black second) is:
.
Probability of selecting a blue ball first, .
Since the selection is without replacement, the total number of balls remaining is 59.
Probability of selecting a black ball second, given the first was blue, .
The probability of the outcome (Blue first, Black second) is:
.
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