Use your graphic display calculator to write down the equation of the regression line for y on x in the form y = ax + b .

Use your equation to estimate the number of calories that a person will burn during a 17 minute walk.

State whether your answer to part (b) is reliable. Give a reason for your answer.

y = 14.9x – 80     (A1)(A1)     (C2)

Notes: Award (A1) for 14.9x and (A1) for –80. Award at most (A0)(A1) if not given in the form of an equation.

[2 marks]

14.9 × 17 – 80     (M1)

Note: Award (M1) for substitution in their equation from part (a).

173.3 calories     (A1)(ft)     (C2)

Note: Accept 173 and 170 even if no working is seen.

[2 marks]

Reliable. 17 min is in the range of given values for x or correlation coefficient (r) is 0.989…     (A1)(R1)     (C2)

Notes: Do not award (A1)(R0). Alternative acceptable reasons using correlation:

Correlation coefficient close to 1

Strong positive correlation

Strong linear correlation

Strong positive association between the variables

Strong relationship between the variables.

This question was an opportunity for candidates to show effective use of the GDC and many correct answers were seen in parts (a) and (b).

This question was an opportunity for candidates to show effective use of the GDC and many correct answers were seen in parts (a) and (b).

Part (c) was unusual in that questions of this nature, in the past, have focused on values outside of the range of given values of x. For correct reasoning, candidates were required to identify that 17 was in the range of values given for x in the table. Identifying that 17 was between 15 and 20 minutes was sufficient whereas identifying that 173 was between 125 and 200 was clearly not sufficient. Alternative reasons which focused on the correlation coefficient being either strong positive or close to one were seen and were accepted.