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Using the 68-95-99.7 rule
PROBLEM: The random variable
* = the stopping distance of a randomly
selected emergency stop for a pickup
truck on dry pavement from a speed of
62 mph can be modeled by a normal
distribution with u = 155 ft and
o= 3 ft. Use the 68-95-99.7 rule
to approximate:
(a) P(x > 158)
(b) The probability that a randomly
selected emergency stop is between 149 ft
and 152 ft.

Respuesta :

Using the Empirical Rule, it is found that the desired probabilities are given as follows.

a) P(x > 158)  = 0.16.

b) P(149 < x < 152) = 0.135.

What does the Empirical Rule state?

It states that, for a normally distributed random variable:

  • Approximately 68% of the measures are within 1 standard deviation of the mean.
  • Approximately 95% of the measures are within 2 standard deviations of  the mean.
  • Approximately 99.7% of the measures are within 3 standard deviations of the mean.

Additionally, considering the symmetry of the normal distribution, 50% of the measures are below the mean and 50% are above.

Item a:

158 is one standard deviation above the mean, hence the probability is given by, considering that 32% of the measures are more than 1 standard deviation from the mean:

P(x > 158) = 0.5 x 0.32 = 0.16.

Item b:

Between one and two standard deviations below the mean, hence:

P(149 < x < 152) = 0.5 x (0.95 - 0.68) = 0.5 x 0.27 = 0.135.

More can be learned about the Empirical Rule at https://brainly.com/question/24537145

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