There are 107 children in the third grade who go on a spring outing, 78 of them bring mineral water, 77 of them bring fruit, and each of them brings at least one piece. How many people in the third grade bring both mineral water and fruit?
三年级有107个小朋友去春游，带矿泉水的有78人，带水果的有77人，每人至少带一样．三年级既带矿泉水又带水果的有几人？
<gadget id="calculator">77 - 107</gadget>
<output>-30</output>

<gadget id="calculator">78 + (-30)</gadget>
<output>48</output>

<result>48</result>