① Reading a frequency tableNo calculator
A frequency table shows how many times each value occurs. The total frequency is the number of values altogether.
② Tally chartsNo calculator
Count the tally marks in each row to find the frequency. Each group of five is four lines crossed by a fifth.
③ Mean from a frequency tableCalculator useful
Multiply each value by its frequency, add these up, then divide by the total frequency.
④ Median and range from a frequency tableNo calculator
Use the running total of the frequencies to find the middle value.
⑤ Missing values and percentagesCalculator useful
Use the total frequency to find a missing frequency, or to write a frequency as a percentage.
⑥ Grouped frequency tablesCalculator usefulCfE 4th Level
When there are lots of different values, put them into groups. Whole-number data is written like 10 – 19 (10 to 19 inclusive). Measured data is written like 10 ≤ t < 20, which means 10 or more but less than 20. To estimate the mean, use the midpoint of each group.
Key steps
Total frequency: add all the frequencies.
Mode: the value with the highest frequency.
Mean: (add up value × frequency) ÷ total frequency.
Median: find the middle position, then use a running total of the frequencies to see which value it falls in.
Grouped data: 10 – 19 includes 10 and 19. 10 ≤ t < 20 includes 10 but not 20. Estimated mean = total of (midpoint × frequency) ÷ total frequency.