00:01
Section 2 .6, problem number 28, we're dealing with a decrease in bacteria.
00:05
So we have bacteria, but they've been exposed to an antibiotic.
00:09
Okay, so when an antibiotic is induced to a culture of 20 ,000 bacteria, the number of bacteria decreases exponentially.
00:16
After 12 hours, i have 5 ,000.
00:19
So i start, so i start this problem with 20 ,000 bacteria, and then i'm told that after 12 hours, i end up with 5 ,000.
00:31
So that's progress in the decrease of bacteria.
00:34
Write an exponential equation.
00:36
So i'm looking for something y equal y -sub -0, e to the k -t.
00:42
Okay, i know my initial value is 20 ,000.
00:45
So this is going to be y equal 20 ,000, e to the k -t.
00:52
And i furthermore know that what happens at 12 hours, when t is 12, y is equal to 5 ,000.
00:59
So i know that 5 ,000 has to eat.
01:02
Equal 20 ,000 e and so after 12 hours so that's 12k this is going to help me solve for that constant k so you're going to have 5 ,000 divided by 20 ,000 is equal to e to the 12k you can simplify this as was it 5 over 20 so there's be one -fourth right so when you simplify this you get one -fourth so 1 4th is equal to e to the 12k, and so then it just take the natural log.
01:58
So the natural log of 1 4th is equal to 12k...