we have that
set of data [8, 12, 15, 17, 18]
step 1
Find the mean
[8+ 12 + 15 + 17 + 18]/5-------> 70/5------> 14
step 2
for each number: subtract the Mean and square the result
(8-14)²----->36
(12-14)²----> 4
(15-14)²----> 1
(17-14)²----> 9
(18-14)²----> 16
step 3
work out the mean of those squared differences
[36+4+1+9+16]/5-----> 66/5-----> 13.2----> this value is called the "Variance"
step 4
Take the square root of that
standard desviation=√13.2-----> 3.63-------> 4
the answer is
4
