I set up a formula within a Word table "=AVERAGE(LEFT)" on a school pupil
report to help staff to quickly complete an average score. In most cases the
boxes to the left contain a figure, sometimes a box may contain "n/a" where a
grade is not applicable. Sometimes this formula seems to work, but others it
does not and I am unable to establish any logical pattern.

Does anyone have any clues to what is wrong?