Daniel O. answered • 10/23/12

Math and Physics Tutor, with a math and physics degree

We can't answer the question without knowing what the initial temperature is. I can give you a formula to use, which will allow you to work out the answer.

Let T represent the temperature at any time, and T_{0} be the initial temperature (at 1pm), and let x be the number of hours past 1pm. Since the temperature drops 4 degrees every hour, we need to subtract 4 times the number of hours (ie, 4*x or 4x) from the initial temperature at 1pm, T_{0}, thus:

T = T_{0} - 4x

Now to find x, the number of hours it'll take to reach -1 degrees, so when T = -1 degrees:

-1 = T_{0} - 4x

Now, rearrange to find x (steps: add 1 to both sides, then add 4x to both sides, then divide by 4, to leave us x):

-1 + 1 = T_{0} - 4x +1 =====> 0 = T_{0} - 4x +1

0 + 4x = T_{0} - 4x + 4x +1 =====> 4x = T_{0} +1

4x/4 = (T_{0} +1)/4 =====> x = (T_{0} +1)/4

Now, just put it whatever the initial temperature is at 1pm, and solve for x, the number of hours it'll take to reach -1 degrees.

Daniel O.

Ah. I see that I was about a month too slow!10/23/12