The ratio of the number of workers at construction sites A and B is 7:5. Now 650 workers are transferred from construction site A to construction site B. The ratio of the number of workers at construction sites A and B becomes 3:4. How many people are there in construction site A?
甲乙两个工地工人人数比是7：5，现在从甲工地调650人去乙工地，甲乙两工地人数比变为3：4，原来甲工地有多少人？
<gadget id="calculator">3 + 4</gadget>
<output>7</output>

<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">7 + 5</gadget>
<output>12</output>

<gadget id="calculator">5 / 12</gadget>
<output>5/12 = around 0.416667</output>

<gadget id="calculator">(4/7) - (5/12)</gadget>
<output>13/84 = around 0.154762</output>

<gadget id="calculator">650 / (13/84)</gadget>
<output>4_200</output>

<gadget id="calculator">7 / 12</gadget>
<output>7/12 = around 0.583333</output>

<gadget id="calculator">4_200 * (7/12)</gadget>
<output>2_450</output>

<result>2_450</result>