There are black and white balls in a cloth bag, and there are 16 white balls, the probability that any one you touch is exactly white is (1/4), how many black balls are there?
一个布袋中有黑白两种颜色的球，白色球有16个，任意摸一个恰好是白球的可能性是(1/4)，则黑球有多少个．
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">16 / (1/4)</gadget>
<output>64</output>

<gadget id="calculator">64 - 16</gadget>
<output>48</output>

<result>48</result>