Xiao Ming used a 20-meter-long rope to measure the distance between the bridge deck and the water surface of a bridge. He folded the rope in half and then hung it to the water surface. As a result, the rope was still 1 meter higher than the bridge deck. What is the distance between the bridge deck and the water?
小明用一根20米长的绳子去量一座桥的桥面与水面的距离，他把绳子对折再对折后垂到水面，结果绳子还高出桥面1米．桥面与水面的距离是多少米？
<gadget id="calculator">20 / 4</gadget>
<output>5</output>

<gadget id="calculator">5 - 1</gadget>
<output>4</output>

<result>4</result>