In order to work out the mean, we add all the values together and then divide by how many values we had. In this case we had
(27 + 25 + x)/3 = 28
To work out what the third day (x) was, we must work backwards and do the opposite.
If finding the mean was adding then dividing, to find the value, we must multiply and then subtract.
Instead of diving by 3, we multiply by 3
28 x 3 = 84
Next we subtract the two values we already have, from 84
84 - 27 = 57
57 - 25 = 32 minutes
On the third day, Greg took 32 minutes to get to work.
