Teacher Qin bought 25 water-based pens at the department store, paid 50 yuan, and got back 7.5 yuan. How much is each water-based pen?
秦老师到百货大楼买了25支水性笔，付出50元，找回7.5元，每支水性笔多少钱？
<gadget id="calculator">50 - 7.5</gadget>
<output>42.5</output>

<gadget id="calculator">42.5 / 25</gadget>
<output>1.7</output>

<result>1.7</result>