The ratio of A and B's deposits is 7:5. If B is given 650 yuan from A's deposit, the ratio of A and B's deposits is 3:4. How much is A's deposit?
甲、乙两人存款金额的比是7：5，如果从甲的存款里给乙650元，这时甲、乙两人存款金额的比是3：4，原来甲有存款多少元．
<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>

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

<result>2_450</result>