If a certain coin is flipped, the probability that the coin will land heads is 1/2. If the coin is flipped 5 times, what

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If a certain coin is flipped, the probability that the coin will land heads is 1/2. If the coin is flipped 5 times, what is the probability that it will land heads up on the first 3 flips and not on the last 2 flips?

A. 3/5
B. 1/2
C. 1/5
D. 1/8
E. 1/32


OA E

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BTGmoderatorDC wrote:
Fri Oct 14, 2022 12:56 am
If a certain coin is flipped, the probability that the coin will land heads is 1/2. If the coin is flipped 5 times, what is the probability that it will land heads up on the first 3 flips and not on the last 2 flips?

A. 3/5
B. 1/2
C. 1/5
D. 1/8
E. 1/32


OA E

Source: GMAT Prep
We want P(heads on 1st AND heads on 2nd AND heads on 3rd AND tails on 4th AND tails on 5th)
= P(heads on 1st) x P(heads on 2nd) x P(heads on 3rd) x P(tails on 4th) x P(tails on 5th)
= 1/2 x 1/2 x 1/2 x 1/2 x 1/2
= 1/32

Answer: E

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The question stipulates one pattern,

HHHTT

There are 2^5 = 32 possible patterns

So the answer must be 1/32

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BTGmoderatorDC wrote:
Fri Oct 14, 2022 12:56 am
If a certain coin is flipped, the probability that the coin will land heads is 1/2. If the coin is flipped 5 times, what is the probability that it will land heads up on the first 3 flips and not on the last 2 flips?

A. 3/5
B. 1/2
C. 1/5
D. 1/8
E. 1/32


OA E

Source: GMAT Prep
Solution:

The probability that the first 3 flips are heads and last 2 flips are tails is:

P(HHHTT) = (1/2)^5 = 1/32.

Answer: E

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