Put all the numbers in order from least to greatest.
Then find where the middle is.. once you've placed them in order it should be 14.5. (I draw a line down the middle of the number)
You have two separate halves now.
Find the middle of the two halves, but since you have 4 numbers on each side you'll have to add two of the numbers together on each side and divide by two to get the number in the middle.
For the half on the least numbers side you'll add 11 and 11.5. This equals 22.5 then divide by 2 and this gives you 11.25.
For the half on the greater side you'd add 17 and 18. This equal 35 then divide by 2 and this gives you 17.5.
The last step is to subtract 11.25 from 17.5 and this will give you the IQR.
