The weight of a Siberian tiger is about 4 times that of an ostrich and 9 times that of a penguin. An ostrich weighs 90 kilograms. How much does a penguin weigh?
一只东北虎的重量大约是一只鸵鸟的4倍，是一只企鹅的9倍，一只鸵鸟90千克，企鹅重多少千克？
<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">90 * (4/9)</gadget>
<output>40</output>

<result>40</result>