The distance between the two places is 125 kilometers. Two cyclists start from the two places at the same time and go towards each other. The speed of A is 15 kilometers per hour, and the speed of B is 10 kilometers per hour. A has a dog and starts at the same time. The dog The running speed is 20 kilometers per hour. When the dog meets B, it returns to run to A. When the dog meets A, it runs to B again. The dog runs back and forth between the two until the two meet. How many kilometers has the dog run so far?
两地相距125千米，两个骑自行车的人同时从两地出发相向而行，甲的速度每小时15千米，乙的速度每小时10千米，甲有一只狗和他同时出发，狗跑的速度是每小时20千米，当狗与乙相遇后，又返回向甲跑，当狗与甲相遇后，又向乙跑去，狗在这二人之间来回跑，直到二人相遇为止，问这只狗一共跑了多少千米？
<gadget id="calculator">15 + 10</gadget>
<output>25</output>

<gadget id="calculator">125 / 25</gadget>
<output>5</output>

<gadget id="calculator">20 * 5</gadget>
<output>100</output>

<result>100</result>