A woodpecker can eat 836 pests in 4 days, and a swallow can eat 840 pests in a week. How many more pests do woodpeckers eat per day on average than swallows?
啄木鸟4天能吃836只害虫，燕子一周能吃840只害虫．啄木鸟平均每天比燕子每天多吃多少只害虫？
<gadget id="calculator">836 / 4</gadget>
<output>209</output>

<gadget id="calculator">840 / 7</gadget>
<output>120</output>

<gadget id="calculator">209 - 120</gadget>
<output>89</output>

<result>89</result>