A piece of cloth, 12% of the total length is used for the first time, and 38% of the total length is used for the second time, leaving 40 meters. How many meters is this piece of cloth?
一匹布，第一次用去全长的12%，第二次用去全长的38%，还剩40米．这匹布原有多少米？
<gadget id="calculator">12 / 100</gadget>
<output>3/25 = around 0.12</output>

<gadget id="calculator">38 / 100</gadget>
<output>19/50 = around 0.38</output>

<gadget id="calculator">1 - (3/25) - (19/50)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">40 / (1/2)</gadget>
<output>80</output>

<result>80</result>