There are 15 small balls in the box, so that the possibility of drawing a yellow ball from the box is (1/5), how many yellow balls should be in the box.
盒子里有15个小球，要使从盒子里摸出黄球的可能性是(1/5)，盒子里应有黄球多少个．
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">15 * (1/5)</gadget>
<output>3</output>

<result>3</result>