A person has three different bags and four different books. The...

To ensure no bag is empty, exactly one bag must contain 2 books and the other two bags must contain 1 book each.

The number of ways to choose 2 books out of 4 to be kept together is $^{4}C_{2} = 6$

Now, we have 3 units (one pair of books and two single books) to be distributed into the 3 different bags.

The number of ways to distribute these 3 units into 3 bags is $3! = 6$

Total number of ways = $6 \times 6 = 36$

Answer: $36$