The temperature on Monday is −4°C. On Tuesday, it is 13° colder. What is the temperature on Tuesday?
The temperature on Tuesday is -4°C - 13°C = <<-4-13=-17>>-17°C. Answer: \boxed{-17}.
To find the temperature on Tuesday, we need to subtract 13°C from the temperature on Monday.
The temperature on Monday is -4°C, so subtracting 13°C from it gives us:
-4°C - 13°C = -17°C
Therefore, the temperature on Tuesday is -17°C.