The back-to-back stem-and-leaf diagram shows the annual salaries of 19 employees at each of two companies, Petral and Ravon. Petral 30 | 0 0 3 31 | 1 2 2 8 9 9 32 | 0 4 5 5 33 | 3 5 7 34 | 0 1 35 | 3 36 | 8 Ravon 30 | 2 6 31 | 1 5 32 | 0 0 2 33 | 0 4 8 9 34 | 1 1 3 4 6 35 | 3 36 | 7 9 Key: 2|31|5 means $31200 for a Petral employee and $31500 for a Ravon employee. The median salary of the Ravon employees is $33800, the lower quartile is $32000 and the upper quartile is $34400.

Mark scheme

Marking points from the official mark scheme (May/June 2024). The mark or mark type is shown in brackets.

1. [B1] Clearly identified, e.g. Q2, med. Accept 32k.
2. [M1] 33300 < UQ ≤ 33700 – 31100 < LQ < 31200 Implied if both quartile values are stated and an appropriate IQR is calculated accurately.
3. [A1] WWW Ignore $ signs. If M0 scored, SC B1 for 2300 WWW. If key ignored consistently: B0 Median = 320 SC M1 325 < UQ < 335 – 311 < LQ < 312 SC A1 23.
4. [B1] All five key values for R plotted accurately in standard format using a linear scale with at least three linear values. Labelled R. Condone whiskers through box or at corners of boxes or extending ½ square beyond limit. Scale no less than 1 cm = $1000. Daylight rule applied to vertical lines of box.
5. [B1FT] All five key values for P, FT from (a), plotted accurately in standard format using a linear scale with at least three linear values. Labelled P. Condone whiskers through box or at corners of boxes or extending ½ square beyond limit. Scale no less than 1 cm = $1000. Daylight rule applied to vertical lines of box.
6. [B1] Whiskers not through box (condone ½ square in box) for either, not drawn at corners of boxes. single linear scale for the diagram and labelled 'salaries' (OE) and $. If only one plot attempted, SC B1 for meeting all the requirements above.
7. [B1] Do not accept 'values'. Must identify median and reference either the extreme value (anomaly, outlier, 36 800) or the skew in context (e.g. concentrated in lower values, positive skew).