8,9,8,11 mean: median: mode: range

Mean: add all numbers together and divide by the amount of numbers there are.
8 + 9 + 8 + 11 = 36
36/4 = 9
mean = 9

Median: Find the middle number. Since in this case it has an even amount of numbers, add the two middle numbers and divide by 2
8 + 9 = 15
15/2 = 7.5
median = 7.5

Mode: The number that shows up the most 
Mode  = 8

Range: Subtract the smallest number from the largest number
11 - 8 = 3
Range = 3

hope this helps