设：原来每小时加工x个零件.
200÷x÷2＝300÷(x+2)
x=200(x+2)/600
x=(200x+400)÷600
x=(600/200x)+600/400
x=1/3x+2/3
x-1/3x=2/3
2/3x=2/3
x=2/3÷2/3
x=1