Question: I would love to understand how to solve this problem: Rosie can run 10 miles per hour for 3 hours. After that, she runs 5 miles per hour. How many miles can she run in 7 hours?
Can you explain?
Answer: 
For the first 3 hours, Rosie runs 10 miles per hour, so she runs 10*3=30 miles.
However, she still has 7-3=4 hours left to room.
For the next 4 hours, she runs 5 miles per hour, so she runs 5*4=20 miles.
In total she runs 30+20=50 miles.