Question

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In order to estimate the average electricity usage per month, a sample of 125 residential customers...

In order to estimate the average electricity usage per month, a sample of 125 residential customers were selected, and the monthly electricity usage was determined using the customers' meter readings. Assume a population variance of 12,100kWh2. Use Excel to find the 98% confidence interval for the mean electricity usage in kilowatt hours. Round your answers to two decimal places and use ascending order.

Electric Usage
765
1139
714
687
1027
1109
749
799
911
631
975
717
1232
806
637
894
856
896
1272
1224
621
606
898
723
817
746
933
595
851
1027
770
685
750
1198
975
678
1050
886
826
1176
583
841
1188
692
733
791
584
1163
593
1234
603
1044
1233
1178
598
904
778
693
590
845
893
1028
975
788
1240
1253
854
1185
1164
741
1058
1053
795
1198
1240
1140
959
938
1008
1035
1085
1100
680
1006
977
1042
1252
943
1165
1014
912
791
612
935
864
953
667
1005
1063
1095
1086
810
1032
970
1099
1229
892
1074
579
754
1007
1116
583
763
1231
966
962
1132
738
1033
697
891
840
725
1031

Solutions

Expert Solution

Solution:

We are given that a sample of 125 residential customers electricity usage per month. We have to use Excel to construct 98% confidence interval for the mean electricity usage in kilowatt hours.

Population Variance =

Thus population standard deviation

Formula:

We use excel commands to find sample mean and margin of Error E

For sample mean:

=AVERAGE( select numbers)

for Margin of Error E

=CONFIDENCE.NORM( alpha , std_dev , Size )

where

alpha = 1 -c = 1- 0.98 = 0.02

Std_dev =

Size = n = 125

Thus we get:

=CONFIDENCE.NORM(0.02, 110 , 125 )

=22.89

Electric Usage
765
1139
714
687
1027
1109
749
799
911
631
975
717
1232
806
637
894
856
896
1272
1224
621
606
898
723
817
746
933
595
851
1027
770
685
750
1198
975
678
1050
886
826
1176
583
841
1188
692
733
791
584
1163
593
1234
603
1044
1233
1178
598
904
778
693
590
845
893
1028
975
788
1240
1253
854
1185
1164
741
1058
1053
795
1198
1240
1140
959
938
1008
1035
1085
1100
680
1006
977
1042
1252
943
1165
1014
912
791
612
935
864
953
667
1005
1063
1095
1086
810
1032
970
1099
1229
892
1074
579
754
1007
1116
583
763
1231
966
962
1132
738
1033
697
891
840
725
1031

Thus

Thus 98% confidence interval for  the mean electricity usage is:

milcah answered 1 year ago
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