An urn contains 10 black and 5 white balls. Two balls are drawn from the urn one after the other without replacement. What is the probability that both drawn balls are black?
Explanation
Step 1: Define the Total Number of Balls
The urn contains:
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Black balls: 10
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White balls: 5
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Total balls: 10+5=15
Step 2: Probability of the First Draw
Let B1 be the event that the first ball drawn is black.
The probability of drawing a black ball is:
P(B1)=Total number of ballsNumber of black balls=1510=32
Step 3: Probability of the Second Draw
Let B2 be the event that the second ball drawn is black. Since the first ball was black and not replaced, the counts change:
The conditional probability P(B2∣B1) is:
Step 4: Calculate the Combined Probability
The probability that both balls are black is the product of the individual probabilities:
P(B1∩B2)=P(B1)×P(B2∣B1)
Now, let's simplify the fraction:
P(B1∩B2)=3×142×9=4218
Reducing to the simplest form:
Final Answer
The probability that both drawn balls are black is: