Water is composed of hydrogen and oxygen in a weight ratio of 1:8. How many kilograms of oxygen is contained in 7.2 kilograms of water?
水是由氢和氧两种元素按1：8的重量比组合成的，7.2千克水中含有氧元素多少千克．
<gadget id="calculator">1 + 8</gadget>
<output>9</output>

<gadget id="calculator">8 / 9</gadget>
<output>8/9 = around 0.888889</output>

<gadget id="calculator">7.2 * (8/9)</gadget>
<output>6.4</output>

<result>6.4</result>