There are three numbers whose average is 3, if one of the numbers is changed to 10, then the average of these three numbers is 5. How much is this changed?
有三个数，它们的平均数是3，如果把其中一个数改为10，那么这三个数的平均数就是5．这个被改动的数是几？
<gadget id="calculator">5 * 3</gadget>
<output>15</output>

<gadget id="calculator">3 * 3</gadget>
<output>9</output>

<gadget id="calculator">15 - 9</gadget>
<output>6</output>

<result>6</result>