The formula for claculating mean is expressed as
Mean = sum of terms/number of terms
Without the outlier,
sum of terms = 20 + 21 + 27 + 34 + 37 + 39 + 42 = 220
number of terms = 7
Mean = 220/7 = 31.43
With an outlier of 11,
sum of terms = 11 + 20 + 21 + 27 + 34 + 37 + 39 + 42 = 231
number of terms = 8
Mean = 231/8 = 28.88
The mean was reduced due to the outlier
The median is the middle term when the terms are arranged in ascending or descending order. In ascending order without the outlier, the terms are
20, 21, 27, 34, 37, 39, 42
Median = 34
With an outlier of 11, the terms are
11, 20, 21, 27, 34, 37, 39, 42
Median = (27 + 34)/2 = 30.5
The median changed
The mode is the term with the highest frequency. With or without the outlier, the mode remains the same. Thus, the mode does not change.
Therefore,
the correct option is
Mean and median
