Question

For a certain class, the following data table compares how many students have a brother or a sister. What is the probability that a randomly chosen student from the class is an only child?
Has a brother Does not have a brother
Has a sister 2 5
Does not have a sister 13 6

Answer 1

Only children are those with neither a brother nor a sister: that's the 6 in the bottom-right cell. Total students = 2+5+13+6 = 26.

Probability = 6/26 = 3/13 ≈ 0.2308 (about 23.1%).