Umm 8/12 or 2/3 .......................................................................
The mean is the average of the numbers, so if x = all 11 numbers added together, then you have the equation:
x / 11 = 7, so x = 77 (this is all of the numbers added together)
if the number 13 is removed, the equation becomes:
(77 - 13) / 10 = M (M is the new mean)
so the new mean is 6.4