Selena reads a book with 400 pages. Harry reads a book with 20 fewer than half the number of pages Selena's book has. How many pages are in the book of Harry? Let's think first. Chain of thought:
Half the number of pages of Selena is 400 / 2 = 200. Therefore, Harry's book has 200 - 20 = 180 pages.
Therefore, the answer is 180.