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A bag contains 4 red balls and 5 blue balls. Two balls are drawn at random without replacement. If the first ball drawn is blue, what is the probability the second ball is also blue?
A bag contains 4 red balls and 5 blue balls. Two balls are drawn at random without replacement. If the first ball drawn is blue, what is the probability the second ball is also blue?
Correct Answer – Option 2 : \(\frac 1 2\)
Concept:
If S is a sample space and A is a favourable event then the probability of A is given by:
\(\rm P(E)=\dfrac{n(A)}{n(S)}\)
Calculation:
Total balls in bag = 4 + 5 = 9 balls
Given: Two balls are drawn at random without replacement
After the first ball is drawn and found to be blue, there are now 8 balls left in the bag, 4 of which are blue.
Probability the second ball is blue = \(\frac 4 8 = \frac 1 2\)