"it was so cold yesterday that the temperature only reached 275." which temperature scale is being used? what would be the corresponding temperature on the other two scales?

Answer is: Kelvin.
1) The temperature in degrees Celsius (°C) is equal to the temperature in Kelvin (K) minus 273,15.
T(°C) = T(K) - 273.15 = 275 - 273,15 = 1,85°C.
2) The temperature in degrees Fahrenheit (°F) is equal to the temperature in Kelvin (K) times 9/5, minus 459.67:
T(°F) = T(K) · 9/5 - 459,67 = 275 · 1,8 - 459,67 = 35,33°F.