During the summer vacation, Xiao Fang plans to finish reading the book "100,000 Why" in 20 days, reading 15 pages every day. In fact, she read 20 pages a day, actually a few days in advance.
20-20× 15÷20,
=20-300÷20,
=20- 15,
=5 (days);
A: She actually finished reading it five days in advance.