A Veterinary Surgeon wishes to survey a stratified sample of size 100 from those people who have pets registered at her surgery. The list below shows the strata to be used and the number in each group.
people who own just dogs - 165 ,
people who own just cats - 140 ,
people who own just small mammals - 105,
others, including those who own more than one type of pet - 90 .
Find how many members of each group should be included in the sample.