for question 21 page 166, u guys need to find the midpoint(m) 1st. after getting the (m), then u guys need to X with the frequency (mf). next is kuasa 2 the midpoint and lastly is the m kuasa2 X frequency.
clas interval frequency midpoint mf m2 m2f
4-9 2 6.5 13 42.25 84.5


after kira all the value, only count the mean, variance, standard deviation