Question

A certain illness is spreading

at a rate of 10% per hour.
How long will it take to
spread to 1,200 people if 3
people are initially exposed?
Round to the nearest hour.

Answer 1

The illness is spreading at a rate of 10% per hour -> it is spreading 1.1x faster per hour as 10% more people are infected each time.

Therefore, we can write the amount of people infected as 3 x
`1.1^(n)`, where n is the hour. So, if n equals 1, the amount of people infected is 3 x 1.1 = 3.3 (so when this mark surpasses the 1200 limit, we round up to the nearest whole number)

It will take 1200 : 3 : 1.1 = 363.636364.. (hours)

If it's only 363 hours, the number of people infected will not have reached 1200, as we have .636364 hours left. So, it will take 364 hours.