The times taken, in seconds, by 15 members of each of two swimming clubs, the Penguins and the Dolphins, to swim 50 metres are shown in the following table. Penguins 35 39 42 44 45 45 48 50 56 58 59 61 66 68 72 Dolphins 36 41 43 48 49 49 50 51 54 56 56 60 61 64 71

Mark scheme

Marking points from the official mark scheme (May/June 2024). 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 Penguins 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 Dolphins labelled on same diagram, leaves in order and lined up vertically (less than halfway to next column), no commas or other punctuation. If the correct data for Penguins & Dolphins is transposed, treat as a single error in Penguins and condone in Dolphins.
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. If two separate diagrams drawn: SC B1 if both keys meet these criteria.
5. [B1] Plotted on box.
6. [B1] Plotted on box.
7. [B1] Correct end points of whiskers (36 and 71). Whiskers not through box, not drawn at corners of boxes, diagram labelled.
8. [B1] Reason given in context. Can be reference to either the central tendency or spread.