Question

A chemist claims that he has found a chemical formula that will kill a certain bacteria. He claims it will kill half the bacteria in 40 seconds, and in the next 40 seconds kill half of the remaining half, and so on. If he is correct, and at a certain time there are 30 bacteria still alive, how many bacteria were alive 4 minutes earlier?
PLEASE EXPLAIN CLEARLY !!

Answer 1

Answer:

4 Minutes = 240 seconds = 6*40 seconds

30*(1/2)^6 = 30*1/64 = 30/64 = 15/32 = 0.5

4 minutes later there is approx. 0 to 1 bacteria alive.