Give one-fifth to the sixth grade, and the remaining four-fifths to the third, fourth and fifth grades.

Proportionally, the fifth grade is 5/(3+4+5)=5/ 12, accounting for 5/ 12*4/5= 1/3 of the whole batch of books.

So 40/ (1/3)= 120 copies.

That is, these books *** 120.