Data Management Probability Question venn diagrams

100 students are polled. 60 are non-grads, 20 are union members, and 20 are non-union graduates. How many are neither grad nor union members? Please explain. Easy immediate 10 points

it is evident that each of the subsets is non-overlapping (disjoint)
as n(non-grad) + n(non-union grad) + n(union) = 60+20+20 = 100, the universe

thus n(neither grad nor union) = n(non-grad) = 60 <-------

draw a venn diagram for clearer understanding