The back-to-back stem-and-leaf diagram shows the diameters, in cm, of 19 cylindrical pipes produced by each of two companies, A and B. Company A | Company B ----------|----------- 4 | 33 | 1 2 8 9 8 3 2 0 | 34 | 1 6 8 9 9 8 7 5 4 1 1 | 35 | 1 2 2 3 9 6 5 2 | 36 | 5 6 4 3 1 | 37 | 0 3 4 | 38 | 2 8 Key: 1|35|3 means the pipe diameter from company A is 0.351 cm and from company B is 0.353 cm.

Mark scheme

Marking points from the official mark scheme (May/June 2022). The mark or mark type is shown in brackets.

1. B1 Identified condone Q2. [Median = 0.355]
2. M1 0.365 < UQ ≤ 0.369 – 0.343 < LQ ≤ 0.349. Subtraction may be implied by answer.
3. A1 If 0/3 scored SC B1 for figs Median = 355 IQR = 18. [0.018]
4. B1 All 5 key values for B plotted accurately in standard format using their scale. Labelled B. Check accuracy in the middle of vertical line.
5. B1 FT All 5 key values for A, FT from part 3(a), plotted in standard format accurately using their scale. Labelled A. Check accuracy in the middle of vertical line.
6. B1 Whiskers not through box for both, not drawn at corners of boxes, single linear scale with at least 3 values stated, covering at least 0.34 to 0.38 and labelled diameter (d etc) and cm. Accept as a title.
7. If both plots attempted and plot(s) not labelled, SC B1 for at least 1 fully correct set of values plotted.
8. B1 Single comment comparing spread or central tendency in context. Must reference either diameter or pipes. Not a simple numerical comparison of statistical values such as median, range, IQR or min/max.