Two large and small gears mesh with each other, the gear ratio is 4:1, if the large gear makes 20 revolutions, how many revolutions does the small gear make?
两个互相咬合的大小齿轮，齿数比为4：1，如果大齿轮转20圈，小齿轮转多少圈．
<gadget id="calculator">20 * 4</gadget>
<output>80</output>

<result>80</result>