In a class 30 of students, 22 have a brother and 25 have a sister. There are 2 students who do not have any siblings. What is the probability that a student chosen randomly from the class does not have a sister?
You should do this with a Venn diagram.
Two overlapping circles inside a rectangle
There are 2 with no siblings that leaves 28 with a brother or a sister or both.
Let x be the number with both.
22 have a brother so 22-x have a brother but no sister.
25 have a sister so 25-x have a sister but no brother
so we have 22-x + x + 25-x = 28
Solve that, find x
Draw the vent diagram properly.
Find the desired probability.