Answer: I saw 3/8 on the first day, and there are only 5/8 left. If you read 5/8* 1/3=5/24 the next day. Then the remaining 1-3/8-5/24=5/ 12. Then the reading volume on the third day is 5/12 *1/5 =112, so the total number of pages is 20/( 1.