The point with this question is that if volume 1 is on the left and volume 2 is ...

		maratc on July 19, 2021 \| parent \| context \| favorite \| on: Math Problems for children from 5 to 15 (2004) [pd... The point with this question is that if volume 1 is on the left and volume 2 is on the right, the first page of volume 1 is facing right and the last page of volume 2 is facing left, so the only thing between them is the two covers. Hence, the answer is 4 mm.