Question

answer this question? with formula

Answer 1

sum of all / no. of terms

Answer 2

$average = \frac{sum \: of \: observations}{total \: no \: of \: observatioms}$
$= \frac{9 + 11 + 8 + 20 + 10 + 16 + 12}{7}$
$= \frac{86}{7}$
average is 12.28 millimetres