Question

John recorded the weight of his dog Spot at different ages as shown in the scatter plot below.

Part A:
Write an equation that would describe the line of best fit.


Part B:
Using the line of best fit, make a prediction of Spot's weight after 18 months.

Answer 1

A) y = 1.875x + 1.25

B) 35 pounds

Explanation:

A) We need two points to define a line. To find an equation that would describe the line of best fit, we can use one of the first points and one of the last points. Let's use (2, 5) and (10, 20).

General equation of a line:

y = mx + b

Slope of the line:

m = (20 - 5)/(10 - 2) = 1.875

y-intercept is found replacing a known point and the slope into the general equation:

5 = 1.875*2 + b

b = 5 - 1.875*2 = 1.25

The final equation is:

y = 1.875x + 1.25

where y represents weight (in pounds) and x represents age (in months)

B) At x = 18:

y = 1.875*18 + 1.25 = 35