我要解一个联立微分方程：
x'=0.02x-0.00004xy
y'=0.0004xy-0.04y
x(0)=500
y(0)=200
其中x,y都是t的函数，我输入下面的指令：
DSolve[{x'[t] == 2/100 x[t] - 4/100000 x[t] y[t],
y'[t] == 4/10000 x[t] y[t] - 4/100 y[t], y[0] == 200, x[0] == 500},
{x[t], y[t]}, t]
却发现电脑给我一大堆错误讯息，
想请问是哪里出了问题？谢谢大家。

Solve::ifun: Inverse functions are being used bySolve, so some solutions may not be found; useReduce for complete solution information. (出现三次)General::stop: Further output of Solve will besuppressed during this calculation.DSolve::bvnul: For some branches of the generalsolution, the given boundary conditions lead toan empty solution. (出现两次)