You will sometimes hear people refer to an exponential rate of growth, and there are two different ways you can have an exponential rate of growth. You can have a discrete exponential rate of growth, and you can have a continuous exponential rate of growth. A discreet rate is very straightforward. Let's say that I have $1.00 and it's growing at a certain rate, r, and I have a certain number of time intervals, t. So the rate represents how much my money would grow in discreet intervals of time, t. So, if I had a rate of 100% per year, that would be r and t = 1. Then at the end of one year, I would have $2.00, and that would be a 100% discreet exponential rate of growth. At the end of two years, I would have $4.00. At the end of three years, I would have $8.00 and so on. But what we're especially interested in here is something called continual exponential growth and a very special constant known as Euler's constant, or e. I'm going to show you right now how we can develop an intuition for what this special number e is. Let's suppose that we had our 100% interest rate. And a clever man said, hey, if you're willing to pay me 100% interest for a year, wouldn't you be willing to pay me 50% interest for six months? And the bank would probably say, well, yeah, that seems fair. And they say, okay, well great. So I would like 50% interest for six months and then I would like interest on my interest for another six months. So, if I have a factor of 1 + 1 and I repeat it one time, I will have 2. But let's say I have a factor of (1.5) and I repeat it 2 times, then I'm going to have a result of 2.25. And the same clever man might say, well gee, if you agreed to pay me interest twice a year, wouldn't you agree to pay me 4 times a year including interest on my interest? So what we're doing here is we're saying 1.25 raised to the 4th power or 1.5 raised to the 2nd power, where this value is our rate per unit time and these are our number of time intervals. So you'll notice, this is decreasing and this is increasing, all right? And if we were paid every 3 months, we'd received $2.44 for every dollar. So an obvious question to ask is does this number keep getting bigger forever and ever? As I make this time intervals smaller, does my potential wealth just increase and increase in an unlimited way? And the answer is surprisingly perhaps is no. It does increase, but eventually it levels off. So let's just take a look at what that would look like. If I'm getting paid interest every month, my factor would be 1.08. It would repeat 12 times, so I would have 1.08 to the 12th and the result would be 2.613. If I'm getting paid interest every week, that would be a factor of 1.019 times 52, or 1.019 raised to the 52nd power, which would be, 2.693. If I was paid interest everyday, this would be 1.002739 times 365. And that would be equal to 2.7146. You notice, the numbers are not increasing as rapidly and there are 8,760 hours in a year. So, if I raised, I would be receiving $2.71813. And at the minutes of which there are, let's see, let's say 525,600, I would receive 2.71828. And then of the seconds of which there are 31,536,000 in a year, then I would receive 2.71828. And although this number continues on, dot, dot, dot, to five significant digits, it has stabilized as I get to a minute or a second. This number is known as Euler's constant or e, 2.71828. So, let's consider an example of a problem. Let's consider a baby elephant that grows continuously at a known rate. So let's say I have a baby elephant. It weighs 200 kg and I know that it grows at a continuously compounded rate of 5%. So it has a growth that is continuously compounded, continuous at 5% per year. I want to know what this elephant weighs in three years. It will weigh (200 kg) e to the (.05) times t, which is 3. It would weigh 200 times e to the 0.15, Which is = 232.4 kg. In addition to this very, very valuable concept of e, we also have the concept of log to the base e, Which is actually written ln(x), which stands for natural log. Why is it the natural log? Because it's the log that we use to calculate naturally occurring continuous rates of growth. So let's suppose that we have some rabbits. And these rabbits with unlimited food increase in mass with their babies at the rate of 200% per year. So let's say that we start with a population of male and female rabbits that weighs 10 kg. And they have unlimited food and resources. And what we want to know is if they're increasing at a continuously compounded rate of 200% per year, How many years, Until they weigh as much as the Earth, which would be 5.972 x 10 to the 24 kg. The way that we set up this problem is as follows. We have 5.972 x 10 to the 24 kg = 10 kg times e to the 2t, where 2 is equal to 200%, that's the rate. And t is equal to the number of years required to create a 5.972 x 10 to the 24 kg worth of rabbits, okay? So first, we can divide both sides by 10. So now we have 5.972 x 10 to the 23 = e to the 2t, okay? And now we're going to use a little trick which is that we're going to take log to the base e of both sides of this equation. So we have ln(5.972 x 10 to the 23rd) = 2t, meaning that t is simply equal to the natural log of this number divided by 2. And you can use your pocket calculator, or Excel, or your computer to calculate the natural log of this number and divide by 2. And what you will find is it will take 27.37 years for the rabbits to weigh as much as the Earth. And that is all you need to know about continuously compounded returns and continuous growth e and the natural log. Thank you.