Page 120 - Data Science class 10
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1.3.1. Tally marks
Tally marks help in counting the frequency of occurrence of something. It is used for record keeping.
1 2 3 4 5
It is customary to show tally marks by vertical bars. In case of tally representing 5 numbers, we don’t use five bars
but show that number by 4 vertical bars and fifth bar as a cross line. Think of Roman number system.
Plotting the tally marks and frequency of ball falling in box A in case of both the trials in one table is given below.
Trials Tally marks Frequency of balls dropping in box A (f)
Trials - 1 Seven tally marks 7
Trials - 2 Six tally marks 6
Example 1.1: Creating a frequency table
To create a frequency table, follow the steps given below:
Step 1 Make three columns. The first column contains the data values in ascending order (from lesser to large
values).
Step 2 The second column contains the number of times the data value occurs using tally marks. Count for every
row in the table. Use tally marks for counting.
Step 3 Count the number of tally marks for each data value and write it in the third column.
For example, Rita maintains the record of the number of customers that visit her shop daily using the frequency
table and tally marks.
Day Number of customers Frequency
Monday 18
Tuesday 13
Wednesday 20
Thursday 13
Friday 21
Saturday 27
Sunday 26
1.4. TWO-WAY FREQUENCY TABLE
A two-way table is a statistical table that determines the observed number or frequency for two variables, the rows
indicate one category and the columns indicate the other category. Two-way frequency tables display how many
data points fit in each category.
Two-way frequency tables are a visual representation of the possible relationships between two sets of categorical
data. The categories are labelled at the top and the left side of the table, with the frequency (count) information
appearing in the four (or more) interior cells of the table.
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