###Human: 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?, ### Assistant: Half the number of pages of Selena is 400/2 = 200.
Therefore, Harry's book has 200 - 20 = 180 pages. 
 So the answer is :  180