| Date | May 2018 | Marks available | 2 | Reference code | 18M.1.sl.TZ1.4 |
| Level | SL only | Paper | 1 | Time zone | TZ1 |
| Command term | Estimate | Question number | 4 | Adapted from | N/A |
Question
A scientist measures the concentration of dissolved oxygen, in milligrams per litre (y) , in a river. She takes 10 readings at different temperatures, measured in degrees Celsius (x).
The results are shown in the table.
It is believed that the concentration of dissolved oxygen in the river varies linearly with the temperature.
For these data, find Pearson’s product-moment correlation coefficient, r.
For these data, find the equation of the regression line y on x.
Using the equation of the regression line, estimate the concentration of dissolved oxygen in the river when the temperature is 18 °C.
Markscheme
−0.974 (−0.973745…) (A2)
Note: Award (A1) for an answer of 0.974 (minus sign omitted). Award (A1) for an answer of −0.973 (incorrect rounding).
[2 marks]
y = −0.365x + 17.9 (y = −0.365032…x + 17.9418…) (A1)(A1) (C4)
Note: Award (A1) for −0.365x, (A1) for 17.9. Award at most (A1)(A0) if not an equation or if the values are reversed (eg y = 17.9x −0.365).
[2 marks]
y = −0.365032… × 18 + 17.9418… (M1)
Note: Award (M1) for correctly substituting 18 into their part (a)(ii).
= 11.4 (11.3712…) (A1)(ft) (C2)
Note: Follow through from part (a)(ii).
[2 marks]
