The average of 5 numbers is 7. After Xiao Ming mistakenly regards one of the numbers as 9, the average of the 5 numbers is 8. What is the number that Xiao Ming misunderstood?
有5个数的平均数是7，小明把其中的一个数错看成9后，求得5个数的平均数是8．小明看错的那个数原来是多少．
<gadget id="calculator">8 * 5</gadget>
<output>40</output>

<gadget id="calculator">7 * 5</gadget>
<output>35</output>

<gadget id="calculator">40 - 35</gadget>
<output>5</output>

<gadget id="calculator">9 - 5</gadget>
<output>4</output>

<result>4</result>