Naughty had read 90% of the 170 pages of the book, which meant that Naughty had read 90/19=5267 pages. The average number of pages to read in the remaining four days can be calculated by dividing the total number of pages by the number of days. 170 pages/4 days =45 pages/day. So, on average, Piao Jiao would read 45 pages a day.