There are 48 students in the whole class, 21 of them can't swim, 15 can't ride a bicycle, and 8 can't play table tennis. So how many students in this class can meet these three sports at least?
全班共有学生48个，其中21人不会游泳，15人不会骑自行车，8人不会大乒乓球，那么这个班至少有多少学生这三项运动全会？
<gadget id="calculator">21 + 15 + 8</gadget>
<output>44</output>

<gadget id="calculator">48 - 44</gadget>
<output>4</output>

<result>4</result>