the mean is the average...to find the mean, add up all the numbers, then divide by how many numbers there are.
Example :
ur set of numbers : 1,2,3,4
add up all the numbers and divide by how many there are :
(1 + 2 + 3 + 4) / 4 = 10/4 = 2.5...so 2.5 is ur mean (average)
