Class 8 Maths Data Handling Grouping Data

Grouping Data

A grouped frequency distribution tablerepresents datafor a group instead of a single value. For example, in a class of 50 students, the marks obtained in Mathematics are as follows: 40,22,28,25,34,33,26,46,18,28,21,15,35,41,37,25,18,14,43,21,46,43,38,45,15,14,17,37,42,32,17,30,27,30,34,47,35,39,31,21,37,48,30,27,15,27,27,30,27,21.

 Group Tally Marks Frequency 0-10 0 11-20 |||| |||| 9 21-30 |||||||||||| |||| 19 31-40 |||||||| | 11 41-50 |||||||| | 11
• The groups are called class intervals or class.
• The lowest number in class is called lower class limit while the highest number is called upper class limit. For example, in 11-20, 11 is the lower class limit and 20 is the upper class limit.
• Difference between the upper and lower class limit is called width or size of class interval.

Problem: The weekly wages (in ₹) of 30 workers in a factory are:

830, 835, 890, 810, 835, 836, 869, 845, 898, 890, 820, 860, 832, 833, 855, 845, 804, 808, 812, 840, 885, 835, 835, 836, 878, 840, 868, 890, 806, 840.

Using tally marks, make a frequency table with intervals as 800 – 810, 810 – 820 and so on.

Draw a histogram and answer the following questions.

(i) Which group has the maximum number of workers?

(ii) How many workers earn ₹ 850 and more?

(iii) How many workers earn less than ₹ 850?

Solution:

 Class intervals Tally Marks Frequency 800-810 ||| 3 810-820 || 2 820-830 | 1 830-840 |||||||| 9 840-850 |||| 5 850-860 | 1 860-870 ||| 3 870-880 | 1 880-890 | 1 890-900 |||| 4

(i) 830 – 840 group has the maximum number of workers.

(ii) 10 workers can earn more than ₹ 850.

(iii) 20 workers earn less than ₹ 850.

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