Maths unit A:Random stratified sampling

This is to find out how many people from a small group should be used as a sample when sampling a large population if you only need a certain amount

-You do it 1 group at a time

1. The first group you do the (total in the group/total in the population) x sample size that you want overall out of the whole poulation, then round as normal to find the number needed from that group

2.Repeat for the other groups and add all aswers to make sure they add to desireable group no.

Example: A population of data has 18 from group A, 6 from group B,14 from group C and 12 from group D. How many of these should be from each group?(we need 10 people overall)

A=(18/50) x 10=3.6=4     B=(6/50) x 10=1.2=1    C=(14/50) x 10=2.8=3   D=(12/50) x 10=2.4=2

4+1+3+2=10