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Date November 2018 Marks available 2 Reference code 18N.2.SL.TZ0.T_1
Level Standard Level Paper Paper 2 Time zone Time zone 0
Command term Justify Question number T_1 Adapted from N/A

Question

The marks obtained by nine Mathematical Studies SL students in their projects (x) and their final IB examination scores (y) were recorded. These data were used to determine whether the project mark is a good predictor of the examination score. The results are shown in the table.

The equation of the regression line y on x is y = mx + c.

A tenth student, Jerome, obtained a project mark of 17.

Use your graphic display calculator to write down y ¯ , the mean examination score.

[1]
a.ii.

Use your graphic display calculator to write down r , Pearson’s product–moment correlation coefficient.

[2]
a.iii.

Find the exact value of m and of c for these data.

[2]
b.i.

Use the regression line y on x to estimate Jerome’s examination score.

[2]
c.i.

Justify whether it is valid to use the regression line y on x to estimate Jerome’s examination score.

[2]
c.ii.

Markscheme

54     (G1)

 

[1 mark]

a.ii.

0.5     (G2)

 

[2 marks]

a.iii.

m = 0.875, c = 41.75   ( m = 7 8 , c = 167 4 )         (A1)(A1)

Note: Award (A1) for 0.875 seen. Award (A1) for 41.75 seen. If 41.75 is rounded to 41.8 do not award (A1).

 

[2 marks]

b.i.

y = 0.875(17) + 41.75      (M1)

Note: Award (M1) for correct substitution into their regression line.

 

= 56.6   (56.625)      (A1)(ft)(G2)

Note: Follow through from part (b)(i).

 

[2 marks]

c.i.

the estimate is valid      (A1)

since this is interpolation and the correlation coefficient is large enough      (R1)

OR

the estimate is not valid      (A1)

since the correlation coefficient is not large enough      (R1)

Note: Do not award (A1)(R0). The (R1) may be awarded for reasoning based on strength of correlation, but do not accept “correlation coefficient is not strong enough” or “correlation is not large enough”.

Award (A0)(R0) for this method if no numerical answer to part (a)(iii) is seen.

 

[2 marks]

c.ii.

Examiners report

[N/A]
a.ii.
[N/A]
a.iii.
[N/A]
b.i.
[N/A]
c.i.
[N/A]
c.ii.

Syllabus sections

Topic 4—Statistics and probability » SL 4.4—Pearsons, scatter diagrams, eqn of y on x
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Topic 1—Number and algebra » SL 1.6—Approximating and estimating
Topic 1—Number and algebra
Topic 4—Statistics and probability
Prior learning

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