. A normal population has a mean of 80.0 and a standard deviation of 14.0. a. Compute the probability of a value between 75.0 and 90.0. b. Compute the probability of a value of 75.0 or less. c. Compute the probability of a value between 55.0 and 70.0. 19. Suppose the Internal Revenue Service reported that the mean

a. The probability of a value between 75.0 and 90.0 is 0.40173

b. The probability of a value of 75.0 or less is 0.35942

c. The probability of a value between 55.0 and 70.0 is 0.19712

Step-by-step explanation:

To solve for this we make use of the z score formula.

z = (x-μ)/σ,

where

x = raw score

μ = the population mean

σ = the population standard deviation.

a. Compute the probability of a value between 75.0 and 90.0.

When x = 75

μ =80.0 and σ = 14.0.

z = (x - μ)/σ

z = 75 - 80/ 14

z = -0.35714

z = -0.36 to 2 decimal places

Using the z score table to find the probability

P(x = 75) = P(z = -0.36)

= 0.35942

For x = 90

z = 90 - 80/14

z = 0.71429

z = 0.71 to 2 decimal place

Using the z score table to find the probability

P(x = 90) = P(z = 0.71)

= 0.76115

The probability of a value between 75.0 and 90.0 is:

75 < x < 90

= P( x = 90) - P(x = 75)

= 0.76115 - 0.35942

= 0.40173

Therefore, probability of a value between 75.0 and 90.0 is 0.40173

b. Compute the probability of a value of 75.0 or less.

For x = 75

From the question, we know that

mean of 80.0 and a standard deviation of 14.0.

z = (x - μ)/σ

z = 75 - 80/ 14

z = -0.35714

z = -0.36 approximately to 2 decimal places.

P-value from Z-Table:

P(x ≤ 75) = 0.35942

c. Compute the probability of a value between 55.0 and 70.0.

For x = 55

From the question, we know that

mean of 80.0 and a standard deviation of 14.0.

z = (x - μ)/σ

z = 55 - 80/ 14

z = -1.78571

z = -1.79 approximately to 2 decimal places

Using the z score table to find the probability

P(x = 55) = P(z = -1.79)

= 0.036727

For x = 70

z = 70 - 80/14

z = -0.71429

z = - 0.71 approximately to 2 decimal place.

Using the z score table to find the probability

P(x = 70) = P(z = -0.71)

= 0.23885

The probability of a value between 55.0 and 70.0 is:

55 < x < 70

= P( x = 70) - P(x = 55)

= P( z = -0.71) - P(z = -1.79)

= 0.23885 - 0.03673

= 0.19712