Page 120 - Data Science class 10
P. 120

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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