Let X be a binomially distributed random variable with parameters n=500 and p=0.3. The probability that X is no larger than one standard deviation above its mean is closest to which of the following?

a. 0.579
b. 0.869
c. 0.847
d. 0.680

Respuesta :

Answer:

c. 0.847

Step-by-step explanation:

From the given information;

[tex]X \sim Binomial (500,0.3)[/tex]

Given that n = 500 which is too large, binomial distribution can now be approximated to

[tex]N ( \mu , \sigma^2)[/tex]

where;

[tex]\mu = np[/tex]

[tex]\mu =500 \times 0.3[/tex]

[tex]\mu =150[/tex]

[tex]\sigma^2= np(1-p)[/tex]

[tex]\sigma^2= 500 \times 0.3(1-0.3)[/tex]

[tex]\sigma^2= 150(0.7)[/tex]

[tex]\sigma^2= 105\\[/tex]

[tex]P(X \leq \mu + \sigma ) = ( \dfrac{X-\mu}{\sigma} \leq 1)[/tex]

[tex]P(X \leq \mu + \sigma ) = ( Z \leq 1)[/tex]

[tex]P(X \leq \mu + \sigma ) =\Phi (1)[/tex]

From the z table

[tex]P(X \leq \mu + \sigma ) =0.841[/tex]

Thus, our value is closest to the option c which 0.847

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