Answer: If John read 4/9 of the book, then the number of pages he read is:
4/9 x 72 pages = 32 pages (rounded to the nearest whole number)
To find out how many pages were not read by John, we can subtract the number of pages he read from the total number of pages in the book:
72 pages - 32 pages = 40 pages
Therefore, John did not read 40 pages of the book.