High School

If the mean height is 180 cm and the standard deviation is 4 cm, what percentage of the population would lie between 176 cm and 184 cm?

A. 50%
B. 68%
C. 95%
D. 34%

Answer :

Standard Deviation: Is a measure of how spread out values are in a data set compared to the mean. It is calculated by finding the square root of the variance, which is the average of the squared differences from the mean.

Mean: The average value of a set of numbers. It is calculated by summing up all the numbers in the set and dividing the result by the total number of numbers in the set.

Distribution Curve: is a bell shaped curve that displays the mean with a line down the center of the curve and standards deviations within standard deviations.

See attached file for model of curve, from: https://commons.wikimedia.org/wiki/File:Standard_deviation_diagram.svg

Given the mean and standard deviation we can use a general rule to determine the population between the given lengths.

Generally in a normal distribution:

  • 68% of the data falls between -1σ and +1σ
  • 95% of the data falls between -2σ and +2σ
  • 99.75 of the data falls between -3σ and +3σ

176 cm is 1 standard deviation less than the mean and 184 cm is 1 standard deviation greater than the mean. Using the general rules above, 68% of data falls between -1σ and +1σ. Therefore, the answer to this question would be B. 68%