Polydactyly is a fairly common congenital abnormality in which a baby is born with one or more extra fingers or toes. It is reported in about one child in every 500 . A young obstetrician celebrates her first 100 deliveries. What is the probability that the obstetrician has delivered no child with polydactyly? (Enter your answer rounded to four decimal places.)

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Answer:

There is a 81.86% probability that the obstetrician has delivered no child with polydactyly.

Step-by-step explanation:

There are only two possible outcomes: Either the baby has the anormality, or he hasn't. So we use the binomial probability distribution.

Binomial probability

The binomial probability is the probability of exactly x successes on n repeated trials, and X can only have two outcomes.

[tex]P(X = x) = C_{n,x}.\pi^{x}.(1-\pi)^{n-x}[/tex]

In which [tex]C_{n,x}[/tex] is the number of different combinatios of x objects from a set of n elements, given by the following formula.

[tex]C_{n,x} = \frac{n!}{x!(n-x)!}[/tex]

And [tex]\pi[/tex] is the probability of X happening.

In this problem, we have that:

It is reported in about one child in every 500, so [tex]\pi = \frac{1}{500} = 0.002[/tex].

A young obstetrician celebrates her first 100 deliveries, so [tex]n = 100[/tex]

What is the probability that the obstetrician has delivered no child with polydactyly?

That is P(X = 0)

[tex]P(X = x) = C_{n,x}.\pi^{x}.(1-\pi)^{n-x}[/tex]

[tex]P(X = 0) = C_{100,0}.(0.002)^{0}.(0.998)^{100} = 0.8186[/tex]

There is a 81.86% probability that the obstetrician has delivered no child with polydactyly.

fichoh

Using the principle of binomial probability, the probability that the obstetrician delivers no child with polydactyl is : 0.8186

Recall :

[tex]P(X = x) = nCx \times p^{x} \times q^{n-x} [/tex]

  • p = probability of success = 1 / 500 = 0.002

  • q = 1 - p = 1 - 0.002 = 0.998

  • n = number of deliveries = 100

Probability of delivering no child with polydactyl ; x = 0

Substituting the values into the equation

[tex]P(X = 0) = 100C0 \times 0.002^{0} \times 0.998^{100} [/tex]

[tex]P(X = 0) = 100 \times 1 \times 0.8185668 [/tex]

[tex]P(X = x) = 81.85668 [/tex]

Therefore, the probability that the doctor delivers no child with polydactyl is 0.8186

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