There are many chickens and ducks in the backyard of Aunt Wang’s house. It is estimated that the total number is between 50 and 60. If the ratio of the number of chickens to the number of ducks is 4:5, how many ducks are there?
王大妈家后院饲养许多鸡鸭，估计总数在50～60只之间，如果鸡的只数与鸭的只数比是4：5，鸭有多少只．
<gadget id="calculator">4 + 5</gadget>
<output>9</output>

<gadget id="calculator">5 / 9</gadget>
<output>5/9 = around 0.555556</output>

<gadget id="calculator">54 * (5/9)</gadget>
<output>30</output>

<result>30</result>