my country is the first country to manufacture and use bronze, which is made of metal tin and copper fused in a certain proportion. The science and technology team of our school tried to make some bronzes. First, they smelted copper and tin at a ratio of 5:4. Later, they found that the hardness was not enough, so they checked the information and found that the ratio of copper to tin is generally 4:1. According to this ratio, 2500 bronzes were remade. gram of bronze, how many grams of copper should be added?
我国是最早制造和使用青铜的国家，它是使用金属锡和铜按一定比例熔合而成的．我校的科技小组尝试制作一些青铜，先把铜和锡按5：4的比熔炼，后来发现硬度不够，于是查阅资料发现铜和锡的比一般是4：1，按照这个比重新制作出2500克青铜，求又加入多少克铜？
<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<gadget id="calculator">5 + 4</gadget>
<output>9</output>

<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">1 / 5 / (4/9)</gadget>
<output>9/20 = around 0.45</output>

<gadget id="calculator">2_500 * (9/20)</gadget>
<output>1_125</output>

<gadget id="calculator">2_500 - 1_125</gadget>
<output>1_375</output>

<result>1_375</result>