In a proportional formula, the product of two inner terms is 4, one outer term is (2/5), and the other outer term is how much.
在一个比例式中，两个内项的积是4，一个外项是(2/5)，另一个外项是多少．
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">4 / (2/5)</gadget>
<output>10</output>

<result>10</result>