There are 20 table tennis balls in the lottery box, marked with 1~20 respectively. If you touch one randomly, what is the probability of getting a single ball number?
抽奖箱里有20个乒乓球，分别标着1～20．任意摸一个，摸到单球数的可能性是多少．
<gadget id="calculator">10 / 20</gadget>
<output>1/2 = around 0.5</output>

<result>1/2 = around 0.5</result>