# Exam-Style Question on Correlation

## A mathematics exam-style question with a worked solution that can be revealed gradually

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Question id: 369. This question is similar to one that appeared on an IB AA Standard paper (specimen) for 2021. The use of a calculator is allowed.

A pair of twins, Percy and Patsy, take Maths assessment tests each week. Their teacher records their scores in this table:

Week 1 Week 2 Week 3 Week 4 Week 5 Week 6 Week 7 Week 8
Percy ($$x$$) 52 60 58 61 65 60 70 72
Patsy ($$y$$) 50 60 61 59 64 64 68 73

(a) Find an equation of the regression line of $$x$$ on $$y$$. The equation should be written in the form $$x = ay + b$$.

(b) Find an equation of the regression line of $$y$$ on $$x$$. The equation should be written in the form $$y = ax + b$$

(c) Find the coordinates of the point of intersection of these two lines.

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