In a box, the probability of touching a red ball is (1/5), given that there are 3 red balls in the box, how many balls are there in the box.
在一个箱子里，摸到红球的可能性是(1/5)，已知箱子里有3个红球，箱子中一共有多少个球．
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

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

<result>15</result>