Put 12 balls in a box, so that the probability of touching a white ball is (1/3), how many white balls should be put in the box.
往盒子里放入12个球，要使摸到白球的可能性是(1/3)，盒子里应该放多少个白球．
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">12 * (1/3)</gadget>
<output>4</output>

<result>4</result>