Question

A random sample of 65 high school seniors was selected from all high school seniors at a certain high school. The following scatterplot shows the height, in centimeters (cm), and the foot length, in cm, for each high school senior from the sample. The least-squares regression line is shown. The computer output from the least-squares regression analysis is also shown.
(a) Calculate and interpret the residual for the high school senior with a foot length of 20cm and a height of 160cm .
(b) The standard deviation of the residuals is s=5.9 . Interpret the value in context.
(c) The following histogram summarizes the 65 residuals.Assume that the distribution of residuals is approximately normal with mean 0cm and standard deviation 5.9cm. What percent of the residuals are greater than 8cm? Justify your answer.
(d) Based on your answer to part (c), would it be surprising to randomly select a high school senior from the high school with a foot length of 20cm and a height greater than 165cm ? Justify your answer.

Answer 1

Step-by-step explanation:

a) According to the least-squares regression line, the estimated height for a high school senior with a foot length of 20 cm is:

y = 2.599x + 105.08

y = 2.599(20) + 105.08

y = 157.06

The residual is 160 − 157.06 = 2.94

b) The differences between each data point and its corresponding estimate varies with a standard deviation of 5.9 cm.

c) Calculate the z-score:

z = (x − μ) / σ

z = (8 − 0) / 5.9

z = 1.36

Use a calculator or table to find the probability.

P(Z > 1.36) = 1 − 0.9131 = 0.0869

Therefore, approximately 8.69% of the residuals are larger than 8 cm.

d) Since the z-score is within ±2 standard deviations, it would not be surprising to randomly select a high school senior with a foot length of 20 cm and height of 165 cm.