The incubation period of eggs is about 21 days, and the incubation period of duck eggs is about 28 days. What percentage is the incubation period of eggs shorter than that of duck eggs?
鸡蛋的孵化期约是21天，鸭蛋的孵化期约是28天．鸡蛋的孵化期比鸭蛋少百分之几？
<gadget id="calculator">28 - 21</gadget>
<output>7</output>

<gadget id="calculator">7 / 28</gadget>
<output>1/4 = around 0.25</output>

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