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Problem-Solving and Data AnalysisVery hardReading the meaning of a y-intercept in context

Problem-Solving and Data Analysis practice question

A scatterplot of the ages of 40 trees and their trunk widths has the line of best fit w = 0.6a + 5, where w is width in centimetres and a is age in years. Which statement best interprets the number 5?

  1. A. The model predicts a trunk width of about 5 centimetres for a tree of age 0.Correct
  2. B. Each year adds about 5 centimetres of width.
  3. C. The trees are 5 years old on average.
  4. D. The widest trunk is 5 centimetres.

Answer: A. The model predicts a trunk width of about 5 centimetres for a tree of age 0.

The intercept is the predicted width at a = 0.

Why the other answers are wrong

B. Each year adds about 5 centimetres of width.
Yearly growth is the slope, 0.6.
C. The trees are 5 years old on average.
Average age is not in the equation.
D. The widest trunk is 5 centimetres.
The intercept is not a maximum.

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