The average of three numbers is 19, two of which are 24 and 17, what is the third number.
三个数的平均数是19，其中两个数是24和17，第三个数是多少．
<gadget id="calculator">19 * 3</gadget>
<output>57</output>

<gadget id="calculator">57 - 24 - 17</gadget>
<output>16</output>

<result>16</result>