Question

Analyzing Student Work
Ramona used the regression equation y = .444x – 21.29, where x represents height and y represents shoe size, to predict the approximate height of a man who wears a size 8.5 shoe.

1. y = .444 (8.5) minus 21.29. 2. y = 3.774 minus 21.29. 3. y = negative 17.52.

Ramona determined that her answer was incorrect because a man who is –17.52 inches tall does not make any sense. What was Ramona’s mistake?
She substituted the 8.5 for the wrong variable.
She should have added .444 and 8.5.
The value for y should be positive.
The solution of –17.52 should be the shoe size.

Answer 1

She substituted 8.5 for the wrong variable.

y is shoe size, so set y = 8.5 and solve for x: x = (8.5 + 21.29)/0.444 ≈ 67.11 inches (about 5 ft 7 in).