6. One factor in the development of tennis elbow, a malady that strikes fear in the hearts of all serious tennis players, is the impact-induced vibration of the racket-and-arm system at ball contact. It is well known that the likelihood of getting tennis elbow depends on various properties of the racket used.

Consider the scatter plot of x  racket resonance frequency (Hz) and y  sum of peak-to-peak acceleration

(a characteristic of arm vibration, in m/sec/sec) for n 23 different rackets ( Transfer of Tennis Racket Vibrations into the Human Forearm, Med. Sci. Sports Exercise, 1992: 1134—1140). Discuss interesting features of the data and scatter plot.

considered regressing y  28-day standard-cured strength (psi) against x  accelerated strength (psi).

Suppose the equation of the true regression line is y  1800  1.3x.

a. What is the expected value of 28-day strength when accelerated strength  2500?

b. By how much can we expect 28-day strength to change when accelerated strength increases by 1 psi?

c. Answer part

(b) for an increase of 100 psi.

d. Answer part

(b) for a decrease of 100 psi.