The average of 8 numbers is 50. If one of the numbers is changed to 90, the average becomes 60. What is the changed number?
某8个数的平均数为50，若把其中的一个数改为90，则平均数变为了60，被改动的这个数原来是多少．
<gadget id="calculator">60 - 50</gadget>
<output>10</output>

<gadget id="calculator">10 * 8</gadget>
<output>80</output>

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

<result>10</result>