Here's a good example. A car driver sees a family of ducks crossing the road in front of her. She brakes for 1·5 s and took 1·8 s to stop. What is her reaction time?
The total stopping time was 1·8 s. This is made of two parts: thinking and braking. The braking time was 1·5 s, so the thinking (reaction) time was 0·3 s.
By the way, she stopped in time - lucky she wasn't driving too fast!
Cute photo credit: Sherwood Park & District Chamber of Commerce