A histogram has frequency densities 1, 1, 4, 8 and 6 for the intervals 0–30, 30–60, 60–90, 90–120 and 120–150 seconds. The total frequency for times exceeding 150 seconds is 120.
Estimate the percentage of people who took less than 90 seconds.
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.