There are 2 red balls and 5 yellow balls in a box, and a ball is drawn at random. What is the sum of the probability of drawing a red ball and the probability of drawing a yellow ball?
一个盒子里装有2个红球和5个黄球，任意摸出一个球，摸出红球的可能性与摸出黄球的可能性之和是多少．
<gadget id="calculator">2 + 5</gadget>
<output>7</output>

<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">5 / 7</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">(2/7) + (5/7)</gadget>
<output>1</output>

<result>1</result>