There are 4 red balls and 3 white balls in a pocket. If you draw a ball at random, what is the probability of getting a red ball?
口袋里装有4个红球，3个白球，任意摸出一个球，摸到红球的可能性是多少．
<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>