Two people walk toward each other from both ends of the bridge. A takes 4 minutes to complete the bridge, and B takes 5 minutes to complete the bridge. B's speed is much slower than A's.
两人从桥的两端相向而行，甲用4分钟走完这座桥，乙用5分钟走完这座桥，乙的速度比甲的速度慢多少．
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/4) - (1/5)</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/20) / (1/4)</gadget>
<output>1/5 = around 0.2</output>

<result>1/5 = around 0.2</result>