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At 3 pm, Jennifer went into labor. There is a 70% chance her baby will

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At 3 pm, Jennifer went into labor. There is a 70% chance her baby will  [#permalink]

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New post 29 Jan 2018, 04:41
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Question Stats:

63% (01:36) correct 38% (01:14) wrong based on 70 sessions

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At 3 pm, Jennifer went into labor. There is a 70% chance her baby will be born each hour that she is in labor. What is the probability that her baby will be born at 6 pm on the same day?

(A) 0.027
(B) 0.063
(C) 0.147
(D) 0.27
(E) 0.343

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Re: At 3 pm, Jennifer went into labor. There is a 70% chance her baby will  [#permalink]

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New post 29 Jan 2018, 05:17
Bunuel wrote:
At 3 pm, Jennifer went into labor. There is a 70% chance her baby will be born each hour that she is in labor. What is the probability that her baby will be born at 6 pm on the same day?

(A) 0.027
(B) 0.063
(C) 0.147
(D) 0.27
(E) 0.343


If the probability that the baby is born in an hour is 0.7(70%),
then the probability that the baby is not born in that hour is 0.3

If the baby is to born at 6, the baby can't be born at 4 or 5,
but must definitely be born at 6.
The probability that the baby is born at 6 is \(0.3*0.3*0.7 =\) 0.063(Option B)
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Re: At 3 pm, Jennifer went into labor. There is a 70% chance her baby will  [#permalink]

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New post 29 Jan 2018, 06:24
P(Born)= 0.7; P(not born)= 0.3
for the baby to be born at 6 pm, we have
P(not born 4 pm) * P(not born 5 pm) * P(born 6 pm) = 0.3*0.3*0.7 = 0.063
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Re: At 3 pm, Jennifer went into labor. There is a 70% chance her baby will  [#permalink]

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New post 30 Jan 2018, 10:18
Bunuel wrote:
At 3 pm, Jennifer went into labor. There is a 70% chance her baby will be born each hour that she is in labor. What is the probability that her baby will be born at 6 pm on the same day?

(A) 0.027
(B) 0.063
(C) 0.147
(D) 0.27
(E) 0.343


For the baby to be born at 6 pm, the baby can not be born at 4 pm nor at 5 pm. Note that since the probability that the baby is born at each hour is 0.7, the probability that the baby is not born in that hour is 1 - 0.7 = 0.3. Thus, the probability that the baby is born at 6pm is (0.3) x (0.3) x (0.7) = 0.063.

Answer: B
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Re: At 3 pm, Jennifer went into labor. There is a 70% chance her baby will  [#permalink]

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New post 31 Jan 2018, 04:18
Bunuel wrote:
At 3 pm, Jennifer went into labor. There is a 70% chance her baby will be born each hour that she is in labor. What is the probability that her baby will be born at 6 pm on the same day?

(A) 0.027
(B) 0.063
(C) 0.147
(D) 0.27
(E) 0.343



    • If we want to find the probability that the baby is born at 6pm, we need to consider that fact that the baby could not have been born in the hours 3pm to 4pm, 4pm to 5pm.
    • If the probability of having the baby in an hour = 0.7
      o The probability of not have the baby within that hour = 1 – 0.7 = 0.3
      o Thus, the probability that baby is not born after 3pm and till 4pm = 0.3
      o The probability that baby is not born after 4pm and till 5pm = 0.3
    • The probability that baby is born between after 5pm and at 6pm = 0.7
    • Thus, the overall probability of having the baby at 6pm when the labor starts at 3PM = 0.3 * 0.3 * 0.7 = 0.063

Correct answer: Option B

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