Use your graphic display calculator to write down the equation of the regression line $t$ on $n$.

Write down the value of the Pearson’s product–moment correlation coefficient, $r$.

Use your regression equation to find the amount of time 4 cleaners take to clean the school.

$t =  - 20.1n + 205$

$t = (-20.1046 \ldots )n + (204.755 \ldots )$     (A1)(A1)     (C2)

Notes: Award (A1) for $-20.1$ and $205$ seen,

     (A1) for an equation involving $t$ and $n$.

[2 marks]

$-0.941 (-0.941366…)$     (A2)     (C2)

Notes: Award (A0)(A1) for $+0.941$.

[2 marks]

$-20.1046 \ldots  \times 4 + 204.755 \ldots$     (M1)

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

$124$ (minutes) ($124.337…$)     (A1)(ft)     (C2)

Notes: Follow through from their regression equation found in part (a). Accept $125$ (minutes) ($124.6$).

[2 marks]