Processing the same machine part, team A alone needs 15 hours, team B needs 4 hours to process alone, and team C needs 20 hours to process alone.
加工同一种机器零件，甲队单独加工需15小时，乙队单独加工需4小时，丙队单独加工需20小时，乙队一小时加工的比甲、丙两队一小时共加工的多多少？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/15) + (1/20)</gadget>
<output>7/60 = around 0.116667</output>

<gadget id="calculator">(1/4) - (7/60)</gadget>
<output>2/15 = around 0.133333</output>

<gadget id="calculator">(2/15) / (7/60)</gadget>
<output>8/7 = around 1.142857</output>

<result>8/7 = around 1.142857</result>