The incubation period of ducks is about 28 days, and the incubation period of chickens is less than that of ducks (1/4). How many days does it take for a chicken to hatch?
鸭的孵化期大约是28天，鸡的孵化期比鸭少(1/4)．鸡的孵化期是多少天？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">28 * (3/4)</gadget>
<output>21</output>

<result>21</result>