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Question
In a malaria epidemic, the number of cases diagnosed were as follows:
| Date July | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
| Num | 5 | 12 | 20 | 27 | 46 | 30 | 31 | 18 | 11 | 5 | 0 | 1 |
On what days do the mode and upper and lower quartiles occur?
Solution
| Date | Number | C.f. |
| 1 | 5 | 5 |
| 2 | 12 | 17 |
| 3 | 20 | 37 |
| 4 | 27 | 64 |
| 5 | 46 | 110 |
| 6 | 30 | 140 |
| 7 | 31 | 171 |
| 8 | 18 | 189 |
| 9 | 11 | 200 |
| 10 | 5 | 205 |
| 11 | 0 | 205 |
| 12 | 1 | 206 |
(i) Mode = 5th July as it has maximum frequencies.
(ii) Total number of terms = 206
Upper quartile = `206 xx 3/4`
= 154.5th term
= 7th July
Lower quartile = `206 xx 1/4`
= 51.5th term
= 4th July
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