In Epi cluster sampling how does the sample size come to be 210 ?

The formula for sample size calculation for prevalence in community based studies is:
n = (z x z x p x q)/(dxd)
= (1.96)2(0.5)(0.5)/0. 12
= (3.84)(0.25)/0.01 = 96
Taking design effect =2, the total sample size becomes 96 x2 i.e. 192
For a 30 cluster technique, number of subjects to be selected per cluster = 192/30 = 6.4 (rounded up to 7)

That means we have to select 30 clusters, each with 7 units making a total sample size of 30 x 7 = 210 !!!
Interesting, isn't it ??