A certain class subscribes to two newspapers, "Mathematics Daily" and "Youth Daily". There are 15 people who subscribe to "Mathematics Newspaper", and 20 people who subscribe to "Youth Daily". Among them, 10 people subscribe to both newspapers, and there are 30 people. How many people are there in this class without ordering any newspapers?
某班订《数学报》和《少年报》两种报纸，订《数学报》的有15人，订《少年报》的有20人，其中有10人两种报纸都定了，有30人没订任何报纸，此班有多少人．
<gadget id="calculator">15 + 20</gadget>
<output>35</output>

<gadget id="calculator">35 - 10</gadget>
<output>25</output>

<gadget id="calculator">25 + 30</gadget>
<output>55</output>

<result>55</result>