The average cooling rate of a cup of coffee is 24 °C per minute, and you can begin to sip the coffee when it is 60 °C. How long must you wait before you can begin to sip the coffee if the initial coffee temperature is 156 °C?
Maybe forever because I don't know how you get the temperature to 156 C because all of the fluid would boil away at just over 100 C. But we'll not worry about that; I assume this is just a made up problem and the author of the problem didn't think about that. So you want to cool it from 156 to 60 which is 156-60 = 96C
96C x (1 min/24C) = ? min.
To determine how long you must wait before you can begin to sip the coffee, you need to calculate the time it takes for the coffee to cool from 156 °C to 60 °C at a rate of 24 °C per minute.
First, find the temperature difference between the initial temperature (156 °C) and the sipping temperature (60 °C):
156 °C - 60 °C = 96 °C
Next, divide the temperature difference by the cooling rate to find the time it takes:
96 °C / 24 °C per minute = 4 minutes
Therefore, you must wait for approximately 4 minutes before you can begin to sip the coffee.