Math mistakes in kids' books 1

I found some math mistake in my daughter's bedtime stories this past month. The first comes from "Ask Mia", a storybook from the Math Matters series. This is an excellent story in which the characters are motivated to create a pictograph to convince a newspaper editor to change her idea of what the paper's content should be. On the final pages is a picture of the newspaper, including this puzzle:

Luis's Quiz: If a hen-and-a-half lays an egg-and-a-half in a day-and-a-half, how many eggs does one hen lay in one day?

The incorrect answer of 'one egg' is given. What is the correct answer?