The average of five numbers is 30. If one of the numbers is changed to 50, the average of the five numbers becomes 25. What is the original number changed.
五个数的平均数是30，如果把其中一个数改为50，则五个数的平均数的平均数变成25．所改动的数原来是多少．
<gadget id="calculator">30 - 25</gadget>
<output>5</output>

<gadget id="calculator">5 * 5</gadget>
<output>25</output>

<gadget id="calculator">25 + 50</gadget>
<output>75</output>

<result>75</result>