The following frequency distribution reports electricity cost for sample of 50 twobebroom apartments in albuquerque, new mexico throughout the month of May last year.
Electricity cost

Frequency

$80 upto $100

3

100 to 120

8

120 to 140

12

140 to 160

16

160 to 180

7

180 to 200

4

Total

50

 Estimate the mean cost.
 Estimate the standard deviation.
 Employ the empirical Rule to estimate the proportion of costs in two standards deviations of mean. What are these limits.