Let's start by setting up our equation
with seven consecutive numbers
and then solve for x

x + (x + 1) + (x + 2) + (x + 3) + (x + 4) + (x + 5) + (x + 6) = 147

7x + 21 = 147

      7x = 147 - 21
7x = 126
   x =

126 / 7

 

 x = 18

so the numbers we were looking for are

18 + (18 + 1) + (18 + 2) + (18 + 3) + (18 + 4) + (18 + 5) + (18 + 6)

18, 19, 20, 21, 22, 23, 24

the median, i.e. the middle number is 21

the mean =  

147 / 7

  = 21

median - mean

21 - 21 = 0

The answer to this question is zero