3/18, or simplified, he has a 1/6 chance of grabbing an adventure book.
Step-by-step explanation:
6 + 5 + 4 + 3 = 18. There's 3 adventure books, which makes it so that he has a 3/18 chance of it being an adventure book. How did I simplify? 18 ÷ 3 = 6, 3 ÷ 3 = 1.
