Average

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An average is a number that is "typical" of a group of numbers. An average is found from the group of numbers by arithmetic.

[edit] To find an average

To find the average of N numbers, the N numbers are added and the total is divided by N. In symbols, if the numbers are X1, X2, X3, ... XN, the total is

X1 + X2 + X3 + ... + XN

The total is divided by N to make the average

{X_1 + X_2 + X_3 + ... + X_N} \over N

[edit] Examples

  • Lucy is 5 years old. Tom is 6 years old. Emily is 7 years old. The three numbers are 5, 6 and 7. To find the average number:
    • Add the three numbers :
5+6+7=18  
  • The total is 18. Divide the total 18 by three:
18/3=6. 
  • The average of the three numbers is 6.
The average age of Lucy, Tom and Emily is 6 years old.
  • Lucy, Tom and Emily have a great-grandmother named Joan. Joan is 90 years old. There are four numbers now; 5, 6, 7 and 90. Lucy, Tom, Emily and Joan's average age is 27 years old:
  • The total is 5+6+7+90=108
  • Dividing the total by four: 108/4=27
  • The total of 1350 divided by 12 is 1350/12=112
If the rain is spread over the year evenly, it would be common to have 112 millimeters of rain in a month in Bolivia. This does not show that it rains every month in Bolivia. All the rain in the year could fall in one or two months, or in one week.