Question

A bacteria culture begins with 15 Bactria which double in amount at the end of every hour. How many Bactria are grown during the 12th hour?

Answer 1

First, we will make a list of the bacteria growth during each hour.

Start: 15

1st hour: 30

2nd hour: 60

3rd hour: 120

4th hour: 240

5th hour: 480

6th hour: 960

7th hour: 1920

8th hour: 3840

9th hour: 7680

10th hour: 15360

11th hour: 30720

12th hour: 61440

As you can see, the number of bacteria present is doubled at the end of each hour, as the question states.

However the question refers to the number of bacteria that grow in the twelfth hour and not the total number of bacteria in the twelfth hour.

So the answer will be the subtraction between the bacteria in the twelfth hour minus the bacteria in the eleventh hour.

$61440-30720=30720$

In conclusion, the answer is 30720