Last Sunday, teams of runners took part in a charity event. The time taken, in seconds, to run 50m was recorded, correct to 1 decimal place, for each runner. The times recorded for 11 runners from each of the Gulls and the Herons are shown in the table. Gulls | 7.9 | 8.2 | 8.3 | 8.6 | 8.6 | 8.8 | 9.2 | 9.7 | 9.8 | 10.0 | 10.4 Herons | 9.5 | 9.9 | 8.5 | 8.1 | 9.2 | 10.8 | 8.3 | 9.7 | 9.3 | 9.9 | 8.7

Mark scheme

Marking points from the official mark scheme (May/June 2025). The mark or mark type is shown in brackets.

1. [B1] Correct stem, ignore extra values (not in reverse, not split). If a split stem-and-leaf plot is used (i.e. stem values are repeated), the remaining B marks are available.
2. [B1] Correct Gulls labelled on left, leaves in order from right to left and lined up vertically (less than halfway to next column), no commas or other punctuation.
3. [B1] Correct Herons labelled on same diagram, leaves in order and lined up vertically (less than halfway to next column), no commas or other punctuation. Penalise each error only once in question. E.g. commas in both sets of data. If the correct data for Gulls & Herons is transposed, treat as a single error in Gulls and condone in Herons.
4. [B1] Correct key for their diagram, need both clubs labelled and 'sec' or 's' stated at least once here, or in leaf headings or title. SC: If 2 separate diagrams drawn, max marks: B1 if both stems correct, B1 if Gulls is correct to the left of the stem B0 B1 if both keys correct including 'sec' or 's'
5. [B1] Clearly identified, e.g. Q2, med, m..
6. [M1] 9.7 < UQ < 10.0 – 8.2 < LQ < 8.6. Implied if both quartile values are stated and the appropriate IQR is calculated accurately.
7. [A1] WWW If M0 scored SCB1 for 1.5 WWW.
8. [M1]
9. [A1] If M0 scored, SCB1 for 8.54 WWW.
10. [M1] Substitute values into correct variance formula, any form.
11. [DM1] Rearrange equation to obtain Σy².
12. [A1] Mark final answer. If one or both M marks not awarded, SCB1 for 1918.8 seen as final answer WWW mark final answer.