The mass ratio of A and B substances in an alloy is 4:5, so how much of the mass of A substance accounts for this alloy.
一种合金中A和B两种物质的质量比是4：5，那么A物质的质量占这种合金的多少．
<gadget id="calculator">4 + 5</gadget>
<output>9</output>

<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<result>4/9 = around 0.444444</result>