The number A is (1/2) the sum of the numbers B, C and D, the number B is (1/3) the sum of the other three numbers, and the number C is (1/4) the sum of the other three numbers. Given that the number D is 390, find the sum of the four numbers.
甲数是乙数、丙数、丁数之和的(1/2)，乙数是其余三数之和的(1/3)，丙数是其余三数之和的(1/4)．已知丁数是390，求四个数的和．
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

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

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

<gadget id="calculator">1 - (1/3) - (1/4) - (1/5)</gadget>
<output>13/60 = around 0.216667</output>

<gadget id="calculator">390 / (13/60)</gadget>
<output>1_800</output>

<result>1_800</result>