Question 33
A materials engineer records the length, x x\,x metres, and the mass, y y\,y kg, of each rod in a random sample of 40 rods. The sample contains rods made from two different materials.
The scatter diagram below shows her data.
The product moment correlation coefficient for all 40 rods is 0.51.
a.[1]
The researcher's scatter diagram contains two distinct sections. State what feature of the diagram shows this.
b.[1]
Suggest what distinguishes the two sections.
c.[2]
Explain why fitting a single regression line of y y\,y on x x\,x to all 40 rods would be misleading.
d.[2]
The engineer separates the data by material and finds that the correlation coefficient within each material is greater than 0.51. Explain why this is consistent with the scatter diagram.
2.2 Data Presentation and Interpretation Questions
121 exam-style questions on OCR A Level Maths 2.2 Data Presentation and Interpretation, covering 2.2.1 Tables and diagrams for single variable data, 2.2.2 Area in a histogram, 2.2.3 Scatter diagrams and regression lines, 2.2.4 Informal interpretation of correlation, 2.2.5 Correlation and causation, 2.2.6 Measures of average and spread, 2.2.7 Calculations of mean and standard deviation, 2.2.8 Outliers, 2.2.9 Selecting or critiquing data presentation, and 2.2.10 Cleaning data. Each one has a worked solution and a mark scheme showing where the marks go.