Mr. Chen brought some money to the store to buy exercise books, and it happened to be on sale. This kind of exercise books was sold at a 20% discount. In this way, the money Mr. Chen brought could just buy 100 more copies than the original one. Knowing the original sales price of each exercise book The price is 2.5 yuan, how much did Mr. Chen bring in total?
陈老师带一些钱去商店买练习本，刚好遇到促销，这种练习本打八折销售，这样陈老师带去的钱刚好可以比原来多买100本，已知每本练习本原来的售价是2.5元，陈老师一共带了多少元钱．
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">2.5 * (4/5) * 100</gadget>
<output>200</output>

<gadget id="calculator">1 - (4/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">200 / (1/5)</gadget>
<output>1_000</output>

<result>1_000</result>