The average of five numbers is 68. If one of the numbers is changed to 100, the average of these five numbers becomes 70. What is the number before the change?
五个数的平均数是68，如果把其中一个数改为100，则这五个数的平均数变为70，改动前这个数是多少．
<gadget id="calculator">70 * 5</gadget>
<output>350</output>

<gadget id="calculator">68 * 5</gadget>
<output>340</output>

<gadget id="calculator">350 - 340</gadget>
<output>10</output>

<gadget id="calculator">100 - 10</gadget>
<output>90</output>

<result>90</result>