A histogram is drawn to represent the times, in seconds, taken by a group of people to complete a task. The frequency densities of the four bars are given in the table below.
| Time, ttt (seconds) | Frequency density |
|---|---|
| 0≤t<200 \le t < 200≤t<20 | 1.5 |
| 20≤t<3020 \le t < 3020≤t<30 | 4 |
| 30≤t<5030 \le t < 5030≤t<50 | 3.5 |
| 50≤t<8050 \le t < 8050≤t<80 | 1 |
The number of people who took at least 20 seconds but less than 30 seconds is 40.
Show that 170 people took part.
Estimate the percentage of these people who took less than 40 seconds.
8 exam-style questions on AQA A Level Maths 2.2.1 Single-variable data diagrams. Each one has a worked solution and a mark scheme showing where the marks go.