There are four piles of pears, with an average of 25 pears in each pile. If the first pile is replaced with 80 pears, then the average number of pears in each pile of the four piles is 40. How many pears were there in the first pile?
有四堆梨，平均每堆25个，如果把其中的第一堆改放80个，那么四堆梨平均每堆有40个，第一堆梨原来有多少个．
<gadget id="calculator">40 * 4</gadget>
<output>160</output>

<gadget id="calculator">25 * 4</gadget>
<output>100</output>

<gadget id="calculator">160 - 100</gadget>
<output>60</output>

<gadget id="calculator">80 - 60</gadget>
<output>20</output>

<result>20</result>