There are three skipping ropes, the first one is 25 meters long and 20 meters shorter than the second one, and the third one is 15 meters shorter than the sum of the lengths of the first and second ropes. How long is the third rope?
有三根跳绳，第一根长25米，比第二根短20米，第三根比第一、第二根绳长之和短15米．第三根绳长多少米？
<gadget id="calculator">20 - 15</gadget>
<output>5</output>

<gadget id="calculator">25 + 25 + 5</gadget>
<output>55</output>

<result>55</result>