piece of wood, I don't know its length. Use a rope to measure, and the rope will be 1.5 meters longer; if the rope is folded in half and then measured, it will be 0.4 meters less. How many meters is this rope?
一根木头，不知它的长度．用一根绳子来量，绳子多1.5米；如果将绳子对折后再来量，又少0.4米．这根绳子长多少米？
<gadget id="calculator">1.5 + 0.4</gadget>
<output>1.9</output>

<gadget id="calculator">1 - 0.5</gadget>
<output>0.5</output>

<gadget id="calculator">1.9 / 0.5</gadget>
<output>3.8</output>

<result>3.8</result>