The frequency distribution below shows the distribution for suspended solid concentration (in ppm) in river water of 50 different waters collected in September 2011.
|
Concentration (ppm)
|
Frequency
|
|
20 - 29
|
1
|
|
30 - 39
|
8
|
|
40 - 49
|
8
|
|
50 - 59
|
10
|
|
60 - 69
|
12
|
|
70 - 79
|
7
|
|
80 - 89
|
2
|
|
90 - 99
|
2
|
1. What percentage of the rivers had suspended solid concentration greater than or equal to 70?
2. Calculate the mean of this frequency distribution.
3. In what class interval must the median lie? Explain your answer. (You don't have to find the median)
4. Assume that the smallest observation in this dataset is 20. Suppose this observation were incorrectly recorded as 2 instead of 20. Will the mean increase, decrease, or remain the same? Will the median increase, decrease or remain the same? Explain your answers.