1.

If X is a normally distributed random variable with mean 14 and standard deviation 2 then P (12 < X < 16) is

Answer»

P(12 < X < 16) = 0.84134 - 0.15866 = 0.68268.

Step-by-step explanation:

We are GIVEN that X is a normally DISTRIBUTED random variable with mean 14 and standard deviation 2.

Let X = a random variable

So, X ~ Normal(\mu=14,\sigma^{2} =2^{2})

The z score PROBABILITY distribution for normal distribution is given by;

                                Z  =  \frac{X-\mu}{\sigma}

where, \mu = population mean = 14

            \sigma = standard deviation = 2

Now, Probability that the random variable X is between 12 and 16 is given by = P(12 < X < 16)

         P(12 < X < 16) = P(X < 16) - P(X \leq 12)

     P(X < 16) = P( \frac{X-\mu}{\sigma} < \frac{16-14}{2} ) = P(Z < 1) = 0.84134

     P(X \leq 12) = P( \frac{X-\mu}{\sigma} \leq \frac{12-14}{2} ) = P(Z \leq -1) = 1 - P(Z < 1)  

                                                  = 1 - 0.84134 = 0.15866

The above probability is calculated by looking at the value of x = 1 in the z table which has an area of 0.84134.

Therefore, P(12 < X < 16) = 0.84134 - 0.15866 = 0.68268.

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