Question

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A chemical engineer desiring to study the evaporation rate of water from brine evaporation beds obtained data on the number of inches of evaporation in each of 55 July days spread over 4 years. The data are given in the following stem and leaf plot, which shows that the smallest data value was.02 inches, and the largest .56 inches. 0 2,6 1 1,4 2 1,1, 1,3.3, 4, 5,5, 5, 6,9 .3 | 0,0, 2, 2, 2, 3. 3. 3. 3. 4.4.5.5.5, 6,6, 7, 8, 9 4 0,1,2,2,2,3,4, 4,4,5,5,5,7,8, 8, 8.9,9 5 2,5,6 Find the (a) sample mean: (b) sample median: (e) sample standard deviation of these data. (d) Do the data appear to be approximately normal (e) What percentage of data salues are within standard deviation of the mean

Answer 1

From stem and leaf diagram, the data is

0.02, 0.06, 0.11, 0.14, 0.21, 0.21, 0.21, 0.23, 0.23, 0.24, 0.25, 0.25, 0.25, 0.26, 0.29, 0.30, 0.30, 0.32, 0.32, 0.32, 0.33, 0.33, 0.33, 0.33, 0.34, 0.34, 0.35, 0.35, 0.35, 0.36, 0.36, 0.37, 0.38, 0.39, 0.40, 0.41, 0.42, 0.42, 0.42, 0.43, 0.44, 0.44, 0.44, 0.45, 0.45, 0.45, 0.47, 0.48, 0.48, 0.48, 0.49, 0.49, 0.52, 0.55, 0.56.

a) sample mean = 19.12/55

= 0.34763636363636

b) sample median = 0.35

c) sample standard deviation s is

S_ Ti- T i=1

= 0.11763036324394

d) Yes, the data appear to be approximately normal.

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