Two gears meshing with each other, the large gear has 80 teeth and rotates at 30 revolutions per minute, and the small gear 120 revolutions per minute. How many teeth does the pinion have.
两个互相啮合的齿轮，大齿轮有80个齿，每分钟转30转，小齿轮每分钟120转．小齿轮有多少个齿．
<gadget id="calculator">80 * 30</gadget>
<output>2_400</output>

<gadget id="calculator">2_400 / 120</gadget>
<output>20</output>

<result>20</result>