set of data [161,170,160]
step 1
Find the mean
[161+170+160]/3=163.67 cm
step 2
for each number: subtract the Mean and square the result
(161-163.67)²----->7.1289
(170-163.67)²----> 40.0689
(160-163.67)²----> 13.4689
step 3
work out the mean of those squared
differences
[7.1289+40.0689+13.4689]/(3-1)=30.33
step 4
Take the square root of that
S=√30.33------> 5.51 cm
SE=S/√n--------> 5.51/√3------> 3.18-------> 3.2 cm
the answer is
3.2 cm
see the attached formulas