Toss 2 coins at the same time, what is the probability that both coins come up heads?
同时掷2枚硬币，2枚硬币都是正面朝上的可能性是多少
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<result>1/4 = around 0.25</result>