What is the correct formula for dividing the difference between 450 and 400 by their sum?
450与400的差除它们的和，商是多少的正确列式是多少
<gadget id="calculator">450 + 400</gadget>
<output>850</output>

<gadget id="calculator">450 - 400</gadget>
<output>50</output>

<gadget id="calculator">850 / 50</gadget>
<output>17</output>

<result>17</result>