Put 18 yellow and white balls of the same size in a box, and touch a ball at random, so that the probability of touching a yellow ball is (2/3), how many white balls should be placed.
往盒子里放18个同样大小的黄白两种颜色的球，任意摸一个球，要使摸到黄球的可能性是(2/3)，白球应放多少个．
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">18 * (2/3)</gadget>
<output>12</output>

<gadget id="calculator">18 - 12</gadget>
<output>6</output>

<result>6</result>