If a ball is randomly drawn from a box containing 3 red balls and 4 yellow balls, what is the probability of drawing a yellow ball?
在一个装有3个红球和4个黄球的纸盒里，任意摸出一个球，摸到黄球的可能性是多少．
<gadget id="calculator">4 + 3</gadget>
<output>7</output>

<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<result>4/7 = around 0.571429</result>