There are 50 students in Class 51, 27 can swim, 18 can play musical instruments, and 15 can neither. How many people can both swim and play musical instruments?
五一班共有50名同学，会游泳的有27人，会演奏乐器的有18人，这两样都不会的有15人．既会游泳又会演奏乐器的有多少人？
<gadget id="calculator">50 - 15</gadget>
<output>35</output>

<gadget id="calculator">18 - 35</gadget>
<output>-17</output>

<gadget id="calculator">27 + (-17)</gadget>
<output>10</output>

<result>10</result>