Statistics, Year 7: more practice

5.5

提示Put the numbers in order first, and notice how many there are.

为什么In order: 3, 4, 4, 7, 9, 12. There are six values, so the median is halfway between the 3rd and 4th: (4 + 7) ÷ 2 = 5.5.

As a diagonal line across the first four

提示Think of how tallies are grouped so they are quick to count.

为什么The first four tallies are upright strokes and the fifth crosses them, so each group stands for 5 and can be counted in fives.

So the height of each bar alone shows its frequency

提示Think about what the reader is comparing.

为什么If widths differed, the bigger area of a wide bar could look more important. With equal widths, only the heights change, so the comparison is fair.

21

提示Half a symbol is half of the key's value.

为什么3 × 6 = 18 and half a symbol is 3, so 18 + 3 = 21. Equivalently, 3.5 × 6 = 21.

3½ symbols

提示Divide the number of cars by the number each symbol stands for.

为什么14 ÷ 4 = 3.5, so three whole symbols and one half symbol show 14 cars.

21:15

提示Add the hours first, then deal with the minutes crossing the hour.

为什么18:50 plus 2 hours is 20:50, and plus 25 minutes is 21:15, because 50 + 25 = 75 minutes is 1 hour 15 minutes.

The temperature stayed the same

提示The line goes along but not up or down.

为什么A flat line means no change in the value while time went on, so the temperature was constant over that spell.

3

提示First find the total rise, then the time it took.

为什么The rise is 20 − 14 = 6 °C over 2 hours, so 6 ÷ 2 = 3 °C per hour.

Presenting (organising) the data

提示Think about what you do before you can interpret anything.

为什么The cycle runs: pose a question, collect data, present it in tables or charts, then interpret and conclude. Presenting makes the pattern visible.

8

提示Turn the mean back into a total before adding the new number.

为什么The first total is 6 × 7 = 42. Adding 14 gives 56, and 56 ÷ 7 = 8.