Question

The table below lists the electricity bills (monthly) of Mali Island comprising of 71 customers.

Electricity Bills monthly
52.30	55.61	55.71	58.01	58.41	58.51	58.91	62.33	62.50	62.71
67.13	67.23	69.51	69.67	69.80	69.82	71.34	71.65	71.83	72.15
77.22	72.41	72.59	72.67	75.11	75.71	75.82	79.03	79.06	79.09
79.15	79.28	79.32	79.51	79.62	82.32	82.61	85.09	85.13	85.25
85.31	85.41	85.51	85.58	89.21	89.32	89.49	89.61	89.78	92.41
92.63	92.89	93.05	93.19	93.28	93.91	94.17	94.28	94.31	94.52
94.71	95.32	95.51	104.31	104.71	105.21	105.37	105.71	109.34	115.71
119.38

a. Group the above data using seven 7 class intervals, each of size 10, and display on a frequency table.

b.   Use Microsoft Excel to construct a histogram for the data obtained in (a).

Answer 1

a) The minimum value in this dataset is 52.3 and the maximum is 119.3

We can start the lower limit of the first class at 52. The lower limit of the next class is obtained by adding the class width 10.

We obtain the following limits for 7 classes

Lower limit
52
62
72
82
92
102
112

Next we can see that the electricity bills have a resolution of 0.01. That is the values are measured to an accuracy of 2 decimals. We will get the upper limit of a class by subtracting 0.01 from the lower limit of the next class. For example, the upper limit of class 1 is 62-0.01=61.99

We get the following table

Lower limit	Upper Limit
52	61.99
62	71.99
72	81.99
82	91.99
92	101.99
102	111.99
112	121.99

To get the upper limit of the last class, we get the lower limit of the imaginary 8th class to be 122.

Next we count the number of observations that fall in each interval. For example, the following 7 observations fall within the interval of the first class, 52-61.99

52.3

55.61

55.71

58.01

58.41

58.51

58.91

And hence the frequency of the first class is 7

We get the following frequency table

ans:

class	Frequency
52-61.99	7
62-71.99	12
72-81.99	16
82-91.99	14
92-101.99	14
102-111.99	6
112-121.99	2

b) select the table and use insert-->2D column-->Clustered

Home Insert Page Layout Tell me what you want to do File Formulas Data Review View Help Get Add-ins Recommended2-D Column Charts Pivot Table Recommended Table Illustrations My Add-ins D PivotTables AA ap Tables Add-ins ur A1 class 3-D Column B C D E G class 2 52-61.99 3 62-71.99 4 72-81.99 Frequency 1 7 2-D Bar 12 16 5 82-91.99 14 6 92-101.99 14 3-D Bar 7 102-111.99 6 8 112-121.99 2 10 More Column Charts.. 11 12 н.

to get this raw graph

Frequency 18 16 14 12 10 8 4 2 0 52-61.99 72-81.99 62-71.99 82-91.99 92-101.99 102-111.99 1 12-121.99 CC LC

format as needed

The histogram electricity bills (monthly) of Mali Island 18 16 14 12 10 6 4 2 0 52-61.99 62-71.99 72-81.99 82-91.99 92-101.99 102-111.99 112-12 1.99 Electricity Bills (monthly) Frequency