pair of gears meshing with each other, the driving wheel has 50 teeth and rotates 60 times per minute. The driven wheel has 30 teeth less than the driving wheel, how many revolutions per minute?
一对互相咬合的齿轮，主动轮有50个齿，每分转60转．从动轮比主动轮少30个齿，每分钟转多少转？
<gadget id="calculator">50 * 60</gadget>
<output>3_000</output>

<gadget id="calculator">50 - 30</gadget>
<output>20</output>

<gadget id="calculator">3_000 / 20</gadget>
<output>150</output>

<result>150</result>