Why must a pictogram have a key?

It shows how many items each symbol represents.

When is a line graph suitable?

When data change over time and the points can sensibly be joined.

Where are points plotted on a frequency polygon?

At the midpoints of the class intervals.

How do you draw a stem-and-leaf diagram?

Split each value into stem and leaf, order the leaves, repeat repeated values and add a key.

What is positive correlation?

As one variable increases, the other increases.

What is negative correlation?

As one variable increases, the other decreases.

Where does a line of best fit pass?

Through the mean point (\bar{x},\bar{y}) and close to the points, with about equal points on each side.

What is extrapolation, and why is it risky?

Predicting outside the range of the data; the pattern may not continue.

Name two ways a bar chart can be misleading.

The vertical axis does not start at 0, or the scale is uneven (or axes are not labelled).

Does correlation prove one thing causes another?

No, it only shows they are related.

Representing dataIB MYP Maths Extended: Flashcards

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How do you find a pie chart angle?

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How do you find a pie chart angle?: $\frac{\text{frequency}}{\text{total}}\times360^\circ$
Why must a pictogram have a key?: It shows how many items each symbol represents.
When is a line graph suitable?: When data change over time and the points can sensibly be joined.
Which type of data suits a bar chart?: Categorical or discrete data.
Where are points plotted on a frequency polygon?: At the midpoints of the class intervals.
Midpoint of $20\leq x<30$ ?: $25$
How do you draw a stem-and-leaf diagram?: Split each value into stem and leaf, order the leaves, repeat repeated values and add a key.
In a stem-and-leaf diagram with key $4\mid1$ means $41$ , what does $5\mid8$ stand for?: $58$
What is positive correlation?: As one variable increases, the other increases.
What is negative correlation?: As one variable increases, the other decreases.
Where does a line of best fit pass?: Through the mean point $(\bar{x},\bar{y})$ and close to the points, with about equal points on each side.
What is extrapolation, and why is it risky?: Predicting outside the range of the data; the pattern may not continue.
Name two ways a bar chart can be misleading.: The vertical axis does not start at $0$ , or the scale is uneven (or axes are not labelled).
Which representation shows proportions of a whole?: A pie chart.
Does correlation prove one thing causes another?: No, it only shows they are related.

Exam questions on Representing data

A class of 30 students chose their favourite sport: football 12, swimming 8, tennis 6 and other sports 4.
Maria says that a line graph is the best way to show this data. Explain why she is wrong and suggest a better representation.2 marks
Eleven students scored these marks in a test: 34, 41, 45, 38, 52, 47, 41, 36, 58, 45 and 41. The marks are shown in an ordered stem-and-leaf diagram with stems 3, 4 and 5. The key is 4 | 1 means 41.
Find the range of the marks and state one advantage of a stem-and-leaf diagram over a grouped frequency table.2 marks
A café owner records the highest temperature (in °C) and the number of cold drinks sold on six days. The pairs (temperature, drinks sold) are (14, 20), (18, 35), (21, 48), (25, 60), (28, 78) and (30, 85).
Describe the relationship between temperature and drinks sold, and explain why the owner should not use this data to predict sales on a day when the temperature is $40^\circ$ C.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).