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John tossed a fair coin 3 times. What is the probability that the outcome was "tails" exactly twice?
A. 1/8
B. 1/4
C. 3/8
D. 1/2
E. 9/10
OA C.
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John tossed a fair coin 3 times. What is the probability
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GMATGuruNY
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P(TTH) = 1/2 * 1/2 * 1/2 = 1/8.AAPL wrote:EMPOWERgmat
John tossed a fair coin 3 times. What is the probability that the outcome was "tails" exactly twice?
A. 1/8
B. 1/4
C. 3/8
D. 1/2
E. 9/10
Since H can occur on the 1st, 2nd or 3rd flip, we multiply by 3:
3*(1/8) = 3/8.
The correct answer is C.
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Hi All,
We're told that John tossed a fair coin 3 times. We're asked for the probability that the outcome was "tails" EXACTLY twice. This question can be approached in a number of different ways; sometimes the fastest way to answer these types of Probability questions is to just 'map out' the possibilities.
Since each coin toss has 2 possible outcomes and we're flipping 3 times, there are (2)(2)(2) = 8 possible outcomes. They are:
HHH
HHT
HTH
THH
TTT
TTH
THT
HTT
3 of the 8 possible outcomes have exactly 2 'tails.'
Final Answer: C
GMAT assassins aren't born, they're made,
Rich
We're told that John tossed a fair coin 3 times. We're asked for the probability that the outcome was "tails" EXACTLY twice. This question can be approached in a number of different ways; sometimes the fastest way to answer these types of Probability questions is to just 'map out' the possibilities.
Since each coin toss has 2 possible outcomes and we're flipping 3 times, there are (2)(2)(2) = 8 possible outcomes. They are:
HHH
HHT
HTH
THH
TTT
TTH
THT
HTT
3 of the 8 possible outcomes have exactly 2 'tails.'
Final Answer: C
GMAT assassins aren't born, they're made,
Rich
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Scott@TargetTestPrep
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AAPL wrote:EMPOWERgmat
John tossed a fair coin 3 times. What is the probability that the outcome was "tails" exactly twice?
A. 1/8
B. 1/4
C. 3/8
D. 1/2
E. 9/10
We need to determine the following:
P(TTH) = (1/2)^3 = 1/8
Since TTH can be arranged in 3!/2! = 3 ways, the probability is 3 x (1/8) = 3/8.
Answer: C
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fskilnik@GMATH
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$$? = P\left( {\,{\rm{exact}}\,{\rm{2}}\,\,{\rm{tails}}\,{\rm{in}}\,{\rm{3}}\,{\rm{tosses}}\,} \right) = {{C\left( {3,2} \right)} \over {2 \cdot 2 \cdot 2}} = {3 \over 8}$$AAPL wrote:EMPOWERgmat
John tossed a fair coin 3 times. What is the probability that the outcome was "tails" exactly twice?
A. 1/8
B. 1/4
C. 3/8
D. 1/2
E. 9/10
This solution follows the notations and rationale taught in the GMATH method.
Regards,
Fabio.
Fabio Skilnik :: GMATH method creator ( Math for the GMAT)
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