The average of 3 numbers is 2, if one of the numbers is changed to 4, the average becomes 3. What is the original number that was changed?
某3个数的平均数是2，如果把其中一个数改为4，平均数就变成了3．被改的数原来是多少．
<gadget id="calculator">3 * 3</gadget>
<output>9</output>

<gadget id="calculator">3 * 2</gadget>
<output>6</output>

<gadget id="calculator">9 - 6</gadget>
<output>3</output>

<gadget id="calculator">4 - 3</gadget>
<output>1</output>

<result>1</result>