The average of 5 numbers is 18, if one of the numbers is changed to 17, the average becomes 16. What is this number?
有5个数的平均数是18，若把其中一个数改成17，平均数就变成16．这个数是多少．
<gadget id="calculator">18 * 5</gadget>
<output>90</output>

<gadget id="calculator">16 * 5</gadget>
<output>80</output>

<gadget id="calculator">90 - 80</gadget>
<output>10</output>

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

<result>27</result>