Every sixth visitor to the bookstore get a free calendar. every twentieth visitor gets a free book. which visitor each day will be the first ones to get both the calendar and book?

The 60 visitor will get the calendar and a book.

The 60th visiter
Here’s why—
First, list the multiples of 6 and 20 to find the least common multiple.
6– 6, 12, 18,24,30,36,42,48,54,60,66,72
20– 20,40,60,80,100

The Least common multiple is 60, telling us that the 60th visiter will get a free calendar and book at the same time.