solving word problems

Question

the number of bacteria present decreased from 12,000,000 to 8,000,000 in 2 hours. what was the percent of decrease?

Answer 1

Percent decrease:

 

New population-Old Population/ Old population

 

8000000-12000000/12000000= -.33 x100 = -33.33%

 

The hours is irrelevant unless they are asking for a rate