1,2,9,9,10,11,n
range:13 mode:9
median:9 mean:8
Find n.
Range is the difference between the highest and the lowest number.
Since the lowest number is 1, and the range is 13, you will be able to find the highest number (n).
Once n is found, verify that all the other properties are still valid.
If in doubt, post your answer for checking.