Year 7 Mathematics | Victorian Curriculum 2.0
Data display
Topic 13 | Statistics & Probability | Answer key

Tier 1: basic skills

Fluency

Fluency

    1. Categorical
    2. Discrete numerical
    3. Continuous numerical
    4. Categorical
    5. Continuous numerical
    6. Discrete numerical (values come in fixed jumps)
    7. A: 555, B: 333, C: 222. Total 101010.
    8. 151515
    9. Column graph
    10. Dot plot
    11. 23, 25, 2823,\ 25,\ 2823, 25, 28
    12. Four data values of 777 appeared in the sample.
    13. 404040
    14. It stretches small differences so bars look very different when they are actually close.

Tier 2: mixed practice

Reasoning

Mixed practice

    1. Size 666: 111, Size 777: 444, Size 888: 555, Size 999: 444, Size 101010: 111.
    2. 888 (appears most often).
    3. Roughly symmetrical around 888.
    4. 555 dots.
    5. A line graph would be inappropriate: shoe sizes are discrete, not a continuous change over time.

    Questions 6-9 from the stem-and-leaf plot:

    1. 151515 students.
    2. Lowest 424242; highest 757575.
    3. 535353 (two students scored 535353) and 616161 (two students scored 616161) - both are modes; the data is bimodal.
    4. Range =75−42=33= 75 - 42 = 33=75−42=33.

Tier 3: explain and spot the mistake

How to mark these
Any clear explanation is fine.
Reasoning

Explain and spot the mistake

    1. A line graph would be better. Temperature varies continuously with time, so joining the hourly readings with a line shows the trend clearly. Columns with gaps suggest separate, independent categories rather than a single continuous variable.
    2. Starting the yyy-axis at 494949 exaggerates tiny differences - the 505050-vs-525252 gap becomes several times taller than it should. A reader glancing at the bar heights might think product CCC sells vastly more than AAA, when it’s only 52−5050=4%\tfrac{52 - 50}{50} = 4\%5052−50​=4% more. Always check whether the yyy-axis starts at zero before comparing bar heights.
    3. Usually not. The mode is the most frequent value while an outlier is a value unusually far from the rest. In an extreme case (e.g. a dataset where one far value appears many times) a single value could be both - but in typical distributions the mode sits in the middle of the bulk, not at the tail.
    4. Not in the arithmetic sense - you cannot average “red”, “blue”, “green”. You can count frequencies for each category and quote the mode (the most common category), but the mean and median don’t apply to purely categorical data.

Tier 4: real-world problems

Problem solving

Real-world problems

    1. 272727 students. Column graph: bars for each sport with heights 9,7,5,4,29, 7, 5, 4, 29,7,5,4,2; yyy-axis shows frequency, xxx-axis shows sport.

    2. Line graph (daily values over the week, with days on the xxx-axis). Total customers served: 42+38+45+50+65+80+60=38042 + 38 + 45 + 50 + 65 + 80 + 60 = 38042+38+45+50+65+80+60=380.

    3. Line graph. Maximum at 222 p.m. (272727 degC).

    4. Stem-and-leaf plot:

      Stem | Leaf
        14 | 5 8 9
        15 | 0 0 0 2 3 5 5 6 8
        16 | 0 2
    5. Line graph. It shows the trend (steady growth) over time clearly.

Year 7 Mathematics study companion | Answer key