Plants Vs Zombies in Reality

Originally, I assumed the plants were growing, and the zombies were eating continuously.

Let the number of plants be P. Every 5 hours, the number of plants triples. Without zombies the number of plants in one hour will be, $P \times 3^{1/5}$ and the number of plants after T hours will be $P \times 3^{T/5}$

Every 6 hours, the number of plants halves. Without growth, the number of plants in one hour will be $P \times 0.5^{1/6}$ and the number of plants after T hours will be $P \times 0.5^{T/6}$ .

These effects are independent, so to combine these effects we can multiply the two together. If this were continuous, the answer would be $16 \times 3^{24/5} \times 0.5^{24/6}$ or $\boxed{195}$

These processes aren't continuous though, so the question is simply asking for $16 \times 3 \times 0.5 \times 3 \times 0.5 \times 3 \times 0.5 \times 3 \times 0.5$ which evaluates to $\boxed{81}$

I made a table and solved it. I know it takes lot time but is easy to understand.

Hours--------------------------------Plants

0 ------------------------------------16

5------------------------------------- Triple of 16 = 16 * 3 = 48

6------------------------------------- Half were eaten of 48 = 24 eaten and 24 left

11----------------------------------- Again triple of 24 = 3 * 24 = 72

12------------------------------------- Half were eaten of 72 = 36 eaten and 36 left

17----------------------------------- Again triple of 36 = 3 * 36 = 108

18------------------------------------- Half were eaten of 108 = 54 eaten and 54 left

23----------------------------------- Again triple of 54 = 3 * 54 = 162

Lastly,

24------------------------------------- Half were eaten of 162 = 81 eaten and 81 left

Our 1 day = 24 hours is over and the remaining plants are $\boxed{81}$