Zombies are doubling every 2 days. If two people are turned into zombies today, how long will it tak

Zombies are doubling every 2 days. If two people are turned into zombies today, how long will it take for the population of about 600,000 to turn into zombies?

Let d = every 2 days. We set up the exponential equation
2 * 2^d = 600,000

Divide each side by 2:
2^d = 300000

To solve this equation for d, we type it in our math engine and we get
d = 18.19 (2 day periods)

18.19 * days per period = 36.38 total days

Most problems like this ask you to round to full days, so we round up to 37 days.