Charts and scatter diagrams Cambridge IGCSE Mathematics (9–1) revision
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In plain words
A good chart shows in a second what a table of numbers hides. The skill is reading them properly, and for scatter diagrams, deciding whether two things really go together.
Three things to know
- Bar charts compare amounts. In a pie chart the angle for each slice is its fraction of the total × 360°. A stem-and-leaf diagram keeps the actual values, in order.
- A scatter diagram plots two measurements for each item. Points rising to the right show positive correlation; falling to the right, negative correlation; scattered everywhere, none.
- A line of best fit follows the trend, with roughly as many points above as below, and goes through the mean point. Use it to estimate values inside the range of the data.
Worked example
In a survey of 60 people, 15 chose blue. Find the angle for blue on a pie chart.
- Blue is 15/60 of the total.
- Angle = 15/60 × 360°.
- = 90°.
Tips and tricks
- Correlation doesn't prove that one thing causes the other.
- Don't use a line of best fit to estimate far beyond the data you have.
It lands in your notebook with its questions as flashcards.
Charts and scatter diagrams: 5 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
In a pie chart, what angle represents one quarter of the data?
A quarter of 360°.
On a scatter diagram the points rise from left to right. What is this?
As one quantity increases, so does the other.
What correlation would you expect between hours of revision and test score?
More revision usually goes with higher scores.
What should a line of best fit pass through?
And it should have points balanced on either side.
20 out of 80 people chose tea. What angle shows tea on a pie chart?
20/80 × 360.
Quiz
5 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
3 questions, 6 marks. Write your answers on paper, then check them.
Charts and scatter diagrams
Cambridge IGCSE Mathematics (9–1) 0980 · 6 marks · papermunch.org
Name ______________________________ Date ______________
In a pie chart showing how 120 students travel to school, 40 walk. Find the angle of the sector for walking.[2]
Show answerHide answer
120°. 40/120 × 360.
Describe the correlation you would expect between the age of a car and its value.[2]
Show answerHide answer
Negative correlation: as the age increases, the value decreases.
A pie chart sector of 72° represents 30 people. How many people were surveyed altogether?[2]
Show answerHide answer
150. 72° is one fifth of 360°; 30 × 5.
Answers: Charts and scatter diagrams
- 1. 120°. 40/120 × 360.
- 2. Negative correlation: as the age increases, the value decreases.
- 3. 150. 72° is one fifth of 360°; 30 × 5.