Temperature question again (help!)?

Question

The temperature at 0800 is -3 degree celsius
The temperature at 1400 is 15 degree celsius.

(a) Find the difference between the two temperatures.

The answer is 15 - (-3) = 15 +3
= 18 degree celsius.

Why must I take the temp at 1400 minus the temp at 0800 instead of the other way round which is -3 - (15) = -18? Explain please?

(b) Assuming that the temp rises at a steady rate, find the temperature at 1220.

Please show your workings clearly and explain, thanks a lot! :)

Hmm, sorry again but how to convert 1hr 40min to (1.67 hour)? Thanks...

Answer 1

when they ask for differences, they mean
temp at the end - temp at the beginning

for b)
temp at 0800 = -3
temp at 1400 = 15
rising 18 deg in 6 hours
or 3 deg per hour
let T be temp at 1220 1hr 40min (1.67 hour) before 1400 , then
(15 - T) / 1.67 = rate = 3
15 - T = 1.67 (3) = 5
T = 15 - 5 = 10
it's 10 deg C

Answer 2

A) the spread between -3 and 15 is 18, you got that both ways.
Now, whether it is +18 or -18 tells yo the direction.
+18 is when the temprature RISES from -3 UP to +15 (from 8 AM to 2 PM) if you go from 2PM to 8AM the temp drops hence, a negative 18 degrees.
if the temp had dropped from 15 to -3 then -18 is the appropriate answer.

B) Here you need to deal with the rate at which the temp rises.
We know it is an 18 degree rise over a period of 6 hrs (14-8).
the rate = 18/6 = 3 degrees / hr. Now take the rate and use it to find the temp at 12:20PM.
12:20 - 8:00 = 4 1/3 Hrs or 13/3 hrs

13/3 hrs * 3 degrees / hr = 13 degrees increase

-3 + 13 = 10 degrees celsius is the temp at 12:20 PM

Answer 3

a) It looks like military time 1400 is 2:00 PM and 0800 is 8:00 AM and 2:00 PM is after 8:00 AM on the same day.

b) so in 6 hours the temperature rises 18 degrees or 1 degree every 20 minutes. At 1220 it is 4 hours and 20 minutes after 8:00 AM so it is 4 * 3 + 1 or 13 degrees warmer from -3 degrees. hence it would be 10 degrees.

Answer 4

Differences between data points are always expressed in positive terms. Think "distances" when you read
"differences".
You wouldn't say that someplace is "negative 15 miles" in the opposite direction, would you?

1) Find the difference between 800 and 1400 (1400-800) to get time (t)
2) You already have the difference between -3 and 15 (18)
3) Divide 18 by t to get the temperature change per hour, or rate (r).
4) Find the difference between 800 and 1220 (1220 - 800) to get new time (n)
5) Multiply n by r to get your change (c)
6) Add c to -3 to get your answer.