x+y=240，x=240-y

Taking out a third of the books from the upper level means taking out 1/3x240=80 books. There are (x-80) books on the upper floor.

Taking out one fifth of the books from the lower level means taking out 1/5x240=48 books. There are (y-48) books on the lower floor.

At this time, the books at the upper level are 1 and 1/3 times that at the lower level, that is, (x-80)= 1 and 1/3(y-48).

Substitute x=240-y into the above formula and get y=96 copies.

There are 96 books on the lower floor.