lheiannie07 wrote:There were initially no black marbles in a jar. Subsequently, new marbles were added to the jar. If marbles are drawn at random and selected marbles are not returned to the jar, what is the probability of selecting 2 black marbles in a row?
(1) After the new marbles are added, 50% of all marbles are black.
(2) Among the 10 added marbles, 8 are black.
Statement 1:
Case 1: 1 black marble and 1 green marble, with the result that 50% of the marbles are black
P(selecting 2 black marbles) = 1/2 * 1/1 = 1/2.
Case 1: 8 black marbles and 8 green marbles, with the result that 50% of the marbles are black
P(selecting 2 black marbles) = 8/16 * 7/15 = 7/30.
Since the probability can be different values, INSUFFICIENT.
Statement 2:
Since the total number of marbles is unknown, it is not possible to determine the probability of selecting 2 black marbles.
INSUFFICIENT.
Statements combined:
Only Case 2 satisfies both statements.
In Case 2, P(selecting 2 black marbles) = 7/30.
SUFFICIENT.
The correct answer is
C.
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