The Student Room Group

C3 random..(exponential i think)

2) A cup of coffe at 85'C is place in a freezer at 0'C. The temperature of the coffee decreases exponentially, so that after 5 minutes it is 30'C.
a) what is its temperature after 3 mins?
b) Find how long it will take for the temperature to drop to 5'C

an answer will do for a) i can do that..
but a full answer for b) will be appreciated.. think ive got half of it right.. just cant finish it to find a final answer :redface:

7d) If log(base10)y = 0.7 +2log(base10)x, express y in terms of x
e) If log(base10)y = -0.5 -5log(base10)x, express y in terms of x

any help is appreciated
Reply 1
7d)

logY = log10^0.7 + logX^2
y = x^2 . 10^0.7
Reply 2
7e)

similarly

Y = 1/(x^5.√10)
Reply 3
then i guess 7e) answer is y = 0.316/x^5

still cant do question 2 :frown: