The topic is: Xiaoming's home is away from school 1000 meters, and Xiaoming goes to school at a speed of 80 meters/minute. Four minutes later, Xiao Ming's father found that Xiao Ming didn't bring his Chinese textbook. He chased Xiao Ming at a speed of180m/min and caught up with Xiao Ming on the way.

Notes can be written like this:

Thinking:

How long did it take dad to catch up with Xiaoming?

② How far is it from school when catching up with Xiao Ming?

Equivalence relation:

The distance that Xiao Ming walks is equal to the distance that Dad walks.

(2) The total time for Xiao Ming to walk-the time for Dad to chase =4 minutes.