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