what is the answer to this question: starting at 1:00p.m., the tempature changes -4 degrees per hour. how long will it take to reach -1 degrees?

Question

please help me.

 

Answer 1

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 T₀ 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, T₀, thus:

T = T₀ - 4x

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

-1 = T₀ - 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 = T₀ - 4x +1    =====>    0 = T₀ - 4x +1 

0 + 4x = T₀ - 4x + 4x +1     =====>    4x = T₀ +1

4x/4 = (T₀ +1)/4                =====>    x = (T₀ +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.

Answer 2

An identicalquestion was asked a few weeks ago. You can see my solution here:

https://www.wyzant.com/answers/717/starting_at_1pmthe_temperature_changes_-4_degrees_per_hourhow_long_will_it_take_to_reach_-1degrees

Answer 3

Initial temp?

Assume room temperature. ~23C

-1 is where you will be, -4x: x= hours it will take

23-4x= -1

add 4x and 1 to both sides

23+1= 4x,     x= 24/4, x= 6 hours