Imagine a marathon race with 10,000 runners.
Runners sprint to a gate in a fence (a fast step).
Only one runner gets through at a time (the slowest step).
After the gate, all runners continue to the finish (a faststep).
The gate is equivalent to the rate-determining step: 
    runners (ie, reacting particles) cannot go faster than the
    slowest step allows.

Also use starters for 10 exercise which has several questions based on different examples - could be made into an multiple choice  /. single choice interactive activity.