Shortcut Trick
Use the Assumed Mean Deviation method to solve it mentally.
Let the Assumed Mean be 10.
Sum of deviations = (+2) + (−7) + (+8) + (+7) + (−6) + (−1) + (+7) + (+9) + (+10) + (+5) + (−2) + (+7) + (−8) + (−7) + (+6) + (+1) + (−7) + (−9) + (−10) + (−5) = 0
Since the net deviation is 0, the Actual Mean is exactly equal to the Assumed Mean.
∴ The correct answer is 10.
Alternate Method
Given:
Data = 12, 3, 18, 17, 4, 9, 17, 19, 20, 15, 8, 17, 2, 3, 16, 11, 3, 1, 0, 5
Number of observations (n) = 20
Formula Used:
Mean = Sum of all observations ÷ Total number of observations
Total Sum of 20 observations = 200 Total Count (n) = 20 Mean = 200 ÷ 20 = 10
Calculations:
⇒ Sum = 12 + 3 + 18 + 17 + 4 + 9 + 17 + 19 + 20 + 15 + 8 + 17 + 2 + 3 + 16 + 11 + 3 + 1 + 0 + 5
⇒ Sum = 200
⇒ Mean = 200 ÷ 20
⇒ Mean = 10
∴ The correct answer is 10.
Additional Information
Assumed Mean Method
A shortcut to find the mean using an arbitrary value: Mean = A + (Σd ÷ n), where A is the assumed mean and d is the deviation of each value from A.
Median
The middle value when a data set is ordered from least to greatest. If the number of values is even, the median is the average of the two middle values.
Mode
The number that occurs most frequently in a data set. A set of data may have one mode, more than one mode, or no mode at all.
Range
The difference between the highest and lowest values in a set of numbers. Range = Maximum Value − Minimum Value.