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Since there were 100 houses sold divide this total by 100 to approximate the mean house price of the houses sold. For the standard deviation calculatiion I would use the expression of the variance which is The sum of the x values is approximated by expression (1) above. To approximate the sum of the squares of the x values use the same logic. The first 5 x values are approximately 90 so the sum of their squares is approximately 5 × 90^{2} etc. so the sum of the squares of the x values is approximately
The median is between the 50^{th} and 51^{st} values. You might just say that the median is between 140 and 160 thousand pounds. You might approximate it my the middle of this class, 150 thousand pounds. You might also do the following. There are 5 + 9 + 20 = 34 values before the class containing the median. This class is 160  140 = 20 units long and you need to go 50.5  34 = 16.5 units to arrive at the median value. Thus another approximation of the median is
Harley  


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