There is a batch of coal in the school canteen. If you burn 50kg a day, you can burn it for 20 days. Later, the stove was improved, and the coal burned every day was saved by 20%. How many more days can you burn this batch of coal?
学校食堂有一批煤，如果每天烧50kg可以烧20天，后来改进炉灶，每天烧的煤节约了20%，这批煤可以多烧多少天？
<gadget id="calculator">50 * 20</gadget>
<output>1_000</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">50 * (4/5)</gadget>
<output>40</output>

<gadget id="calculator">1_000 / 40</gadget>
<output>25</output>

<gadget id="calculator">25 - 20</gadget>
<output>5</output>

<result>5</result>