Page 257 - ICSE Math 7

3. Ruchika works in a customer care call centre where the employees keep a record of the number
of minutes each telephone call lasts.

She collects the following data on a particular day:
10, 25, 31, 31, 19, 13, 26, 26, 19, 10, 13, 20, 26, 19, 26, 19, 26, 30, 28, 26

(a) Convert the data into frequency table.
(b) How many minutes does the longest and shortest call last? Also calculate the range.

(c) Calculate the mean, median and mode.
(d) Which central tendency best describes the situation and is useful in estimating the total time
the employees are at work?

4. The number 50, 42, 41, 35, 2x + 10, 2x –8, 12, 11, 8, 6 are arranged in descending order and if
their median is 25, find x.

5. The mean weight of 6 boys in a group is 48 kg. If five boys of the group weigh 51 kg, 45 kg,
49 kg, 46 kg and 44 kg, find the weight of the sixth boy.

Bar Graphs

In the previous class, we have seen how information collected could be first arranged in a frequency
distribution table and then this information could be converted into pictographs or bar graphs.
A bar graph is a pictorial presentation of data which is represented by rectangles of uniform width
with equal spacing between them called bars.

Construction of bar graphs

In a bar graph, each bar or rectangle represents only one value of the numerical data and there are as
many bars as the number of values in the data. Bars are usually drawn vertically on the horizontal
line which is x-axis. The height of the bars depends on the values of the numerical data. We assume
a suitable and convenient scale to decide the height of the bars along y-axis. In order to construct a
bar graph, the following points must be kept in mind.
1. Draw two perpendicular lines and call them as horizontal and vertical axes.

2. Along the horizontal axis, mark the information given in the data like days, weeks, months,
years, subjects, places, etc. at uniform gaps.
3. Select a suitable scale to determine the heights of the bars or rectangles along the vertical
axis. For example, if 1,200 people like cricket, then 1 unit length can be taken to represent
200 people so that a bar of height 6 units can represent 1,200 people.

4. Draw bars or rectangles of equal width and height as determined in the previous point.
These bars should have uniform spacing between them. The figure so obtained is called a bar
graph.

Points to remember

• A bar graph should always have a title.
• The horizontal and vertical axis should be labelled to show what they represent.

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