Nico borrows 3 books from the library on Monday.  On Monday, he reads the first book with a total of 20 pages.  On Tuesday, he reads the second book with a total of 12 pages.  On Wednesday, he reads the third book.  If he has read a total of 51 pages from Monday to Wednesday, how many pages did he read on Wednesday?
From Monday to Tuesday, Nico reads a total of 20 + 12 = <<20+12=32>>32 pages.
On Wednesday, he read a total of 51 - 32 = <<51-32=19>>19 pages.
#### 19