The weights of tea in 70 packets are shown in the following table:
Weights(in grams)200−01201−202202−203203−204204−205205−206Number ofpackets1327181011
Find the mean weight of packets using step-deviation method.
Solution:
Let us choose A=201.5,h=1, then di=xi−201.5 and
ui=(xi−A)h=xi−201.51
Using the Step-deviation method, the given data is shown as follows:
Weight(in grams)Number of packets(fi)Class mark(xi)di=A−xi=201.5−xiui=(xi−201.5)1fiui200−20113200.51113201−20227201.5000202−20318202.5−1−1−18203−20410203.5−2−2−10204−2051204.5−3−3−3205−2061205.5−4−4−4Total∑fi=70∑fiui=−22
N=∑fiui=−22
h=1A=201.5
Mean =A+∑fiuiN×h
=201.5+−2270×1=201.5−0.31=201.19