The temperature coefficient of resistivity of iron is 5.0 ´ 10-3 / °C; that of carbon is -0.50 ´ 10-3 / °C. When an iron wire and a carbon rod, each having the same 10 W resistance at 20°C, are cooled from that temperature to -80°C, the new ratio of the resistance of the carbon rod to the resistance of the iron wire at the lower temperature is