Question

Each minute, a zombie "infects" 4 new people. But the new zombiescannot infect anyone. How many zombies will there be after 5minutes?

Answer 1

Assuming we start with one zombie that can infect others, we can calculate the total number of new zombies using a rule of three:

`\begin{gathered} 1\text{ minute}\to4\text{ new zombies} \\ 5\text{ minutes}\to x\text{ new zombies} \\ \\ (1)/(5)=(4)/(x) \\ \\ x=4\cdot5 \\ x=20 \end{gathered}`

After 5 minutes there will be 20 new zombies. Then, adding the first zombie that infected the others, we have a total of 21 zombies.

In the same way, if we start with x zombies, the total number of zombies after 5 minutes will be 21x (x starting zombies plus 20x new zombies).