sana.noor wrote:Tony's political science final exam consists of eight True/False questions. If Tony guesses on every question, what is the probability that he gets exactly seven questions right?
A) 1/32
B) 1/16
C) 1/8
D) 7/8
E) 31/32
OA is A
P(exactly 7 right) = P(exactly 1 wrong).
P(exactly N times) = P(one way) * total possible ways.
One way:
One way to get exactly 1 wrong is to answer only the 1st question wrong.
P(WRRRRRRR) = 1/2 * 1/2 * 1/2 * 1/2 * 1/2 * 1/2 * 1/2 * 1/2 = 1/2�.
Total possible ways:
WRRRRRRR represents ONE WAY to answer exactly 1 question wrong.
To account for ALL OF THE WAYS to answer exactly 1 question wrong, the result above must be multiplied by the number of ways to arrange the letters WRRRRRRR.
Since W could appear in any of the 8 positions of the arrangement, the total number of ways to answer exactly 1 question wrong = 8.
Thus;
P(exactly 1 wrong) = (1/2�) * 8 = 1/32.
The correct answer is
A.
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