The hour and minute hands are perpendicular to each other at 9 o'clock.
时针和分针在9点多少分互相垂直．
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">1 - (1/12)</gadget>
<output>11/12 = around 0.916667</output>

<gadget id="calculator">30 / (11/12)</gadget>
<output>360/11 = around 32.727273</output>

<result>360/11 = around 32.727273</result>