eqns = {D[y[x],x]+y[x]==0,y[0]==1}
vars = y[x]
xmax = 3
precis=80
{soln1}=DSolve[eqns,vars,x]
{soln2}=NDSolve[eqns,vars,{x,0,xmax},WorkingPrecision->precis*3/4,MaxSteps->Infinity]
yy1 = y[x]/.soln1
yy2 = y[x]/.soln2
Plot[{yy1,yy2},{x,0,xmax},LabelStyle->Medium,AxesLabel->{x,y}]
Plot[Abs[yy1-yy2],{x,0,xmax},LabelStyle->Medium,AxesLabel->{x,error},PlotRange->All]