The mean is the average, add the numbers together and divide by the number of students asked:
Mean = 4 + 15 + 19+ 11 + 6 + 16 + 9 + 15 = 95/8 = 11.875 rounded to the nearest tenth = 11.9
Median is the middle value, list the numbers from smallest to largest:
4, 6, 9, 11, 15, 15, 16, 19
There ia an even number, so find the middle two numbers, add them together and divide by 2:
Median = 11 + 15 = 26 / 2 = 13