Answer
a)convenience sampling.
b)See example below.
c)0.75
d)0.64.
Work Step by Step
a) Here voluntary response or a subgroup from the population is used, hence it is convenience sampling.
b)Students might come from the same ethnic group, and thus then not represent the whole population.
c) By using the addition rule: P(brown or blue)=P(brown)+P(blue)=40%+35%=0.4+0.35=0.75
d)Here we can use the complement rule: P(at least one brown eye)=1-P(no brown eye)=$1-(1-0.4)^6=1-0.6^2=0.64.$
