The average of five numbers is 30, if one of them is changed to 50, the average of five numbers is 25. What is the number changed.
五个数的平均数是30，将其中一个改为50，则五个数的平均数是25．所改的数是多少．
<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>