A certain product was sold at a 20% discount on the price last year, and a 20% profit can be obtained. Since the purchase price this year is 100 yuan lower than last year's purchase price, this year it is sold at the same price as last year at a 25% discount, but a 25% profit can be obtained. So how much is the purchase price this year?
某产品去年按定价打八折出售，能获得20%的利润．由于今年买入的价比去年买入价减少了100元，因此今年按与去年同样定价打七五折出售，却能获得25%的利润．那么今年买入价是多少元？
<gadget id="calculator">75 / 100</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 + (1/4)</gadget>
<output>5/4 = around 1.25</output>

<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

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

<gadget id="calculator">1 + (1/5)</gadget>
<output>6/5 = around 1.2</output>

<gadget id="calculator">(4/5) / (6/5)</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">1 * (2/3)</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">(3/4) / (5/4) / (2/3)</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">1 * (9/10)</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">1 - (9/10)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">100 / (1/10)</gadget>
<output>1_000</output>

<gadget id="calculator">1_000 - 100</gadget>
<output>900</output>

<result>900</result>