x÷（5000+x）=0.8解：x=0.8（5000+x） x=4000+0.8x x-0.8x=4000 0.2x=4000 x=4000÷0.2 x=20000
x÷5000+x=0.8 两边乘5000x+5000x=40005001x=4000x=4000/5001
