17-3

Review of Variance and Standard Deviation
In this lesson, we learned about the statistics variance and standard deviation, which are both used to describe the spread of data about the mean.
- s & o = standard deviation
- s^2 = variance
- E = sum
- xi = numbers
- n = how many you have
- x(with a line over it) = mean
- standard deviation formula: s = sq. root of (E(xi^2)/n) -x^2

Example 1: Find the standard deviation of the data 1, 7, 9, 15.

• n=4; x=8; E(xi^2)=356 *I just listed how many numbers there are(4), the mean(8), and the sum(356). Now I use these numbers to plug into the formula.


• sq. root of (356/4)-4


• answer: s^2= 25; s= 5 *I just divided 356 by 4 and subtracted 64 to get 25 to get the variance(25), and then took the square root to find the standard deviation(5).