Xiao Ming read 20% of the total number of pages on the first day of reading a book, which means that the total number of pages multiplied by 20% equals 20% of the total number of pages. On the second day, the ratio of pages read on the first day was 5:4, which meant that half of the total pages read on the second day was 25% of the total pages. Therefore, Xiao Ming read the total number of pages multiplied by 25% the next day, which was equal to the total number of pages multiplied by 5%. Divide the total number of pages by 5 to get the number of pages that Xiaoming read the next day divided by 5. That is, the total number of pages divided by 5 multiplied by 40% equals the total number of pages multiplied by 10%. Therefore, Xiao Ming read the total number of pages multiplied by 10% the next day, which was equal to the total number of pages multiplied by 5.