There are 40 athletes, 25 of them can wrestle, 20 can fencing, and 10 can neither fencing nor wrestling. How many athletes can wrestle and fencing?
有40名运动员，其中有25人会摔跤，有20人会击剑，有10人击剑、摔跤都不会，既会摔跤又会击剑的运动员有多少人．
<gadget id="calculator">25 + 20</gadget>
<output>45</output>

<gadget id="calculator">40 - 10</gadget>
<output>30</output>

<gadget id="calculator">45 - 30</gadget>
<output>15</output>

<result>15</result>