The tonnage ratio of the two warehouses A and B originally stored rice was 7:5. If 650 tons of rice were transferred from warehouse A to warehouse B, the tonnage ratio of rice stored in the two warehouses was 3:4. The original warehouse A stored rice How many tons?
甲、乙两个仓库原来存放大米的吨数比是7：5，如果从甲仓库调动650吨大米到乙仓库，那么两个仓库存放大米的吨数比是3：4，原来甲仓库存放大米多少吨？
<gadget id="calculator">7 + 5</gadget>
<output>12</output>

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

<gadget id="calculator">3 + 4</gadget>
<output>7</output>

<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">(7/12) - (3/7)</gadget>
<output>13/84 = around 0.154762</output>

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

<result>4_200</result>