# The mean

### The mean - formula

What is the Mean? The mean or average gives an average of a series of numbers. For example, the average body weight of my friends. The formula for calculating the mean is $$\bar{X} ={\sum{X} \over {n}}$$ X with the line on top we read: X bar (eks bar). It stands for the mean, the average of the scores in our sample. X stands for score. The capital Greek letter we read: Sigma. It stands for the Sum of the scores. The n we read: n. It stands for the number of scores in our sample.### The mean -practice example

An experimenter wanted to know what quantity of food young rats eat. weighed the food each ate in 24 hours in grams. He chose 6 rats randomly from the colony of rats in his lab. Here are the data, The symbol for each score is X.X

34

35

39

30

39

40

Looking at the formula above, we add all of scores and divide by the number of scores. The symbol for the number of scores is n. In this case the n is 6. The sum of the scores is 217, ΣΧ=34+35+39*30+39+40=217

Now we divide this by 6, the n, and we find the mean 36.17. $$\bar{X}= {217 \over{6}}= 36.17$$

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