| Weekly wages (in Rs) | 50-55 | 55-60 | 60-65 | 65-70 | 70-75 | 75-80 | 80-85 | 85-90 |
| No. of workers | 5 | 20 | 10 | 10 | 9 | 6 | 12 | 8 |
Calculate:
(i) The mean.
(ii) the modal class
(iii) the number of workers getting weekly wages below Rs. 80.
(iv) the number of workers getting Rs. 65 or more but less than Rs. 85 as weekly wages.
Solution:
We write the given data in cumulative frequency table.
| Class Interval | Frequency (fi) | Class mark (xi) | Cumulative frequency | fixi |
| 50-55 | 5 | 52.5 | 5 | 262.5 |
| 55-60 | 20 | 57.5 | 25 | 1150 |
| 60-65 | 10 | 62.5 | 35 | 625 |
| 65-70 | 10 | 67.5 | 45 | 675 |
| 70-75 | 9 | 72.5 | 54 | 652.5 |
| 75-80 | 6 | 77.5 | 60 | 465 |
| 80-85 | 12 | 82.5 | 72 | 990 |
| 85-90 | 8 | 87.5 | 80 | 700 |
| Total | ∑fi = 80 | ∑fixi = 5520 |
(i) Mean = ∑fixi /∑fi
= 5520/80
= 69
Hence the mean is 69.
(ii) Modal class is the class with highest frequency.
Here the modal class is 55-60.
(iii) The number of workers getting weekly wages below Rs. 80 is 60.
[Check the cumulative frequency column and class interval column. 60 workers get below Rs. 80]
(iv) The number of workers getting Rs. 65 or more but less than Rs. 85 as weekly wages = 72-35 = 37
[Check the cumulative frequency column and class interval column. ]