4. The lengths of 40 leaves of a plant are measured correct to the nearest millimetre, and the data obtained is represented in the following table :
Find the median length of the leaves.
(Hint : The data needs to be converted to continuous classes for finding the median, since the formula assumes continuous classes. The classes then change to
117.5 - 126.5, 126.5 - 135.5, . . ., 171.5 - 180.5.)
The data needs to be converted to continuous classes for finding the median, since the formula assumes continuous classes.
Class |
Frequency
|
Cumulative Frequency |
117.5-126.5 | 3 | 3 |
126.5-135.5 | 5 | 8 |
135.5-144.5 | 9 | 17 |
144.5-153.5 | 12 | 29 |
153.5-162.5 | 5 | 34 |
162.5-171.5 | 4 | 38 |
171.5-180.5 | 2 | 40 |
Therefore, Median class = 144.5-153.5
Lower limit, l = 144.5; Class height, h = 9
Frequency corresponding to median class, f = 12
Cumulative frequency of the class preceding the median class, c.f. = 17
Thus, median length of the leaves is 146.75 mm