The number of bacteria present in a colony is 180 at 12 noon and the bacteria grows at a rate of 22% per hour. How many will be present at 8 p. m.?

Equation:

Solution:

Now 12 noon to 8 pm is 8 hours in total, every hour you've increased your bacteria population by 22%

if you start with population P

after 1 hour we have P * (1+0.22)

after 2 hours we have P * (1+0.22) ^2

after 8 hours we have P * (1+0.22) ^8

therefore since we started with population 180 at 12 noon we have

at 8 pm, 180 * (1+0.22) ^2