There are 170 books in Class A and 30 books in Class B. After how many books are given to Class B by Class A, Class A has 20 more books than Class B?
When Class A is twice as many as Class B, and there are 20 copies, Class B has:
( 170+30-20)÷(2+ 1)
= 180÷3
=60 copies
60-30=30 copies
A: After Class A gave Class B 30 books, Class A had 20 more books than Class B..