Zhang Ming rides a bicycle to and from A and B. It takes 4 hours to go there and 5 hours to return. What percentage is the return speed reduced compared to the go speed?
张明骑车往返于甲、乙两地，去时用4小时，回时用5小时，返回时的速度比去时的速度减少百分之几？
<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>