Complex sentence: Group 3 acted the same as the Group 2 rats until food was introduced on Day 11; then they quickly learned to run to the end of the maze and did as well as the Group 1 rats by the next day.
Split into simpler sentences: Group 3 acted as the Group 2 rats until food was introduced on Day 11. Then they quickly learned to run to the end of the maze and did as well as the Group 1 rats by the next day.