Give 4 ways to choose a 150 students sample from 2700 students using simple random sampling, systematic, stratified and cluster sampling...
Thanks...
It's a statistics subject... :):):);)

Combination 2700 things taken 150 at a time

C_{N,R} = \frac {N!}{(N-R)! \,\times\, \, R!}

where ! Is the factorial operator. I'll let you try to figure out how this is affected by the different types of sampling, but here's a hint:

Wikipedia - Sampling (statistics) (http://en.wikipedia.org/wiki/Sampling_%28statistics%29#Sampling_methods)