(2013•八步区模拟)如图所示的电路中,电源电压恒为3V,只闭合开关S,电流表的示数为0.3A;再闭合开关S1,电流表的示数为0.5A,则电阻R2的阻值为______Ω,通过R1与R2的电流之比为______.