The fast and slow trains start from A and B at the same time and go towards each other. When the fast train travels the entire distance (4/5), the slow train travels the entire distance (5/9), what percentage of the total distance is the distance between the fast and slow trains?
快、慢两车从A，B两地同时出发，相向而行．当快车行了全程的(4/5)时，慢车行了全程的(5/9)，这时快慢车间的距离占全程的几分之几？
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">5 / 9</gadget>
<output>5/9 = around 0.555556</output>

<gadget id="calculator">(5/9) - 1</gadget>
<output>-4/9 = around -0.444444</output>

<gadget id="calculator">(4/5) + (-4/9)</gadget>
<output>16/45 = around 0.355556</output>

<result>16/45 = around 0.355556</result>