There is a piece of wood. I don’t know its length. If you measure it with a rope, the length of the rope is 1.5 meters. If you fold the rope in half and measure it, it is not enough for 0.4 meters. How long is this rope in meters?
有一根木头，不知它的长度，用一根绳子来量，绳子还多1.5米，如果把绳子对折后来量，又不够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>