There are 42 students in the third grade, 31 of them subscribe to "Youth Daily", and 27 of them subscribe to "Fairy Tale News". Each of them subscribes to at least one newspaper. How many students subscribe to both newspapers?
三年级有42名同学，订阅了《少年报》的有31人，订阅了《童话报》的有27人，每人至少订1份报纸，那么两种报都订的同学有多少人．
<gadget id="calculator">31 + 27</gadget>
<output>58</output>

<gadget id="calculator">58 - 42</gadget>
<output>16</output>

<result>16</result>