Question

The amount of water left in a cup after sitting outside in the sun can be modelled by the function A(t) = 120((12)^t/3 where A(t) represents the amount of water in mL and t represents the time passed in hours

a) write down how much water will be there after 24 hours. Round your answer to 2 decimal places.

b) write down how long it takes for the amount of water to get to 15 mL

Answer 1

Huh? Your function increases with time. It must be raining.

Answer 2

Due to the number of people who can't seem to figure out how to type fractions, I guess you mean
A(t) = 120*(1/2)^t/3
That is, half the water evaporates every 3 hours.
(a) 24 hours is 8 half-lives, so 120 * 1/2^8 = 120/128
(b) just solve
120*(1/2)^(t/3) = 15
1/2^(t/3) = 15/120 = 1/8
since 1/8 is 3 half-lives, then it will take 3*3 = 9 hours.