ï»¿ >> Okay class, Professor Anderson here. Let's ask you a question. How old are you in seconds? So how old are you guys? >> 24. >> 24. All right. I'm a little older than 24. I keep telling my kids that I'm 29 on every birthday, and after a while they caught on that maybe that wasn't quite true. Okay. So, 24, that's a great age. How old are you in seconds? Well, let's see if we can figure that out. 24 years, we want to convert that to seconds. So, we want to get rid of the years. What do we know? How many days are in a year? >> 365 point -- >> 365, is that exact? >> No. >> No. What's after the 5? >> Like .49 -- >> .25, right? That little extra bit of a quarter is why we have to do what? >> Leap year. >> Every four years we have to have a leap year. It's interesting, back in the mid-1500s, they hadn't accounted for the leap year, and so the calendar started to shift as opposed to the peak of summer. And they noticed this, and they said, "Oh, this is a problem." And so, all of a sudden, they wiped out like 10 days of October off the calendar [background laughter]. Then they just said, "You know what? We're changing the dates." And I kept thinking, "Oh, those poor kids that had that birthday right in the gap. They just -- that's -- " >> Got kicked over. >> All right. So, 365, that's close enough. There's some digits after that. Every four years we have to add an extra day. Every hundred years we have to do something else. Every 400 years we have to do something else. Okay, we've got to tweak the calendar a little bit. But 365 days in a year. Okay? So now we got rid of years. What about days? How many hours are in a day? There are of course 24 hours in a day. So we get rid of days. How many minutes are in an hour? There are 60 minutes in an hour. And how many seconds in a minute? There are 60 seconds in a minute. So we get rid of hours. We get rid of minutes. And we end up with seconds. And now we just have a bunch of numbers to multiply. So let's multiply them. We've got 24. We've got 365. We have another 24. We have 60. And we have 60. And there's all 1's in the bottom; this is seconds. What is that number? Well, pull out your calculators and calculate that, and let's approximate it here. So we've got 2.4 times 10 to the 1. And we've got 3.7 times 10 to the 2. And then we have another 2.4 times 10 to the 1. And we have a 6 times 10 to the 1. And we have a 6 times 10 to the 1. So, this is approximately what? Well, if I bump this down, then I can bump the next one up. And if I bump that one down, then I can bump the next one up, and we'll leave the last one. And then we just have to count up the 0's. We've got 1, 2, 3, 4, 5, 6. And now we can multiply this out pretty easily, right? We've got 2 times 4 is 8, times 2 is 16, times 10 is 160, times 6 is roughly a billion. And I suspect that the real answer is a little bit less than that. What did you guys get for your real answer? >> 7.57 times 10 to the 8th. >> Okay. So, it is .75 billion. So, that's how old you are in seconds. You can see that our approximation was off by about 25%. You know, we can probably do better than that next time. But you are 750 million seconds old. All right? Maybe you're wishing you had a few of those back just now [background laughter]. But that's how old you are, 750 million seconds.