On a winter day, the outside temperature was negative 24 degrees Fahrenheit and was rising by six degrees an hour. Determine the time it took the temperature to reach zero degrees Fahrenheit.
Here we have a number line, and we want to begin at negative 24 degrees. But then we want to end up at zero degrees. And it says that, every hour, we will rise six degrees, and we want to know how many hours will it take.
So if we would rise six degrees from negative 24 degrees, we would end up at negative 18 degrees, and this would take one hour. And if we would be at negative 18 degrees and then rise six more degrees, we would end up at negative 12. And that took another hour. So we’re at two hours.
And notice as the temperature is rising, we’re moving in the positive direction on the number line, to the right. After another hour, we are now at negative six degrees. And finally, after the fourth hour, we’ll have reached the temperature of zero degrees Fahrenheit. So how many hours did it take? Four hours.