StopLearnStopLearnA curve or a graph of a cummulative frequency is called cumulative frequency curve or give.
Cummulative frequency or give is used for the determination of a median, quartiles, deciles & percentage.
Median: This is a middle term. It is half of a cummulative frequency.
Quartiles:Here, the cummulative frequency is divided into four places.
Deciles: Here, the cummulative frequency is divided into ten places.
Percentiles: Here, the cummulative frequency is divided into hundred places.
Example:1 The frequency distribution of the hundred participant in a high jump competition as shown below.
| Weight | 20 – 29 | 30 – 39 | 40 – 49 | 50 – 59 | 60 – 69 | 70 – 79 |
Solution
To construct the cumulative frequency curve, you need the class mid-point and the class boundary
| Weight(kg) | Frequency (f) | Class mark (x) | Cum. freq. | Class boundary |
| 20 – 29 | 10 | 24.5 | 10 | 19.5 – 29.5 |
| 30 – 39 | 18 | 34.5 | 28 | 29.5 – 39.5 |
| 40 – 49 | 22 | 44.5 | 50 | 39.5 – 49.5 |
| 50 – 59 | 25 | 54.5 | 75 | 49.5 – 59.5 |
| 60 – 69 | 16 | 64.5 | 91 | 59.5 – 69.5 |
| 70 – 79 | 9 | 74.5 | 100 | 69.5 – 79.5 |
N.B: 1st cumulative frequency is the same as first frequency
last cumulative frequency is the same as total frequency
Scale: 1cm to 10 unit on cum. freq axis
2cm to 10 unit on class mark axis
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