A bamboo pole with a length of 4 meters is inserted vertically into a pool. The part of the bamboo pole that enters the mud is 0.4 meters, and the part that is above the water is 0.8 meters. How deep is the pool in meters?
把一根长4米的竹竿垂直插入水池中，竹竿入泥的部分是0.4米，露出水面的部分是0.8米．池水深多少米？
<gadget id="calculator">4 - 0.4 - 0.8</gadget>
<output>2.8</output>

<result>2.8</result>