There are 5 red balls and 2 white balls in the bag, what is the probability of touching the white ball?
袋内装有5个红球和2个白球，摸到白球的可能性是多少．
<gadget id="calculator">5 + 2</gadget>
<output>7</output>

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

<result>2/7 = around 0.285714</result>