Question

The temperture of a mixture decrease at the rate of 1degree per 30 mins the twmperature of mixture at 3oclock was 5degree
At what time will the temperature be 3degree below zero ?
What will be the temperature of mixture at 6oclock?

Answer 1

you want an 8 degree drop.

Each degree takes 30 minutes, so ...

and 6:00 is how many 30-minutes periods after 3:00?

Answer 2

Assuming that the decrease is linear,
we could use 2 ordered pairs of the form (t, d) to find the equation , where t is the time, and d is the temperature in °
how about (3,5) ----> at 3:00 the temperature was 5°
and (4,3)
slope = (3-5)/1 = -2 ---> tells me temp decreases 2° every hour
t = -2d + b
using (3,5)
5 = -6+b
b = 11

d = -2t + 11

a) so when d = -3
-3 = -2t + 11
2t = 14
t = 7 ----> 7:00

b) when t = 6
d = -2(6) + 11 = -1

or
Just use a simple chart:

degree - time
5° ------ 3:00
3° ------ 4:00
1° ------- 5:00
-1° ------ 6:00
-3° ------ 7:00