Would you put $20,000 in this investment? Think again!!!

You have $20,000.00 dollars that you want to invest. A close friend of you offers an outstanding investment opportunity, one that you just can't pass on.
Here is how your friend explains the investment rules:
You're going to put all your money into this account. Every day the amount in your account will either go up by x%, or go down by x%, where x varies daily, randomly, between 0% (meaning you don't win or lose anything) to 99% (but it will never be 100%, meaning that you won't ever double your money or lose everything in a day). Are you still with me?
OK, so far it doesn't sound that attractive. Seems like a toss of a coin. But your friend keeps going with the explanation:
Alright, but here is the deal: with this investment you can have sequences of good days or bad days. These sequences happen continuously and randomly. When you land in a bad sequence, then you'll lose one day but you'll win the next day, guaranteed. BUT, when you land on a good sequence, my dear, you will have 4 (four) consecutive days of winning, followed by one day of losing. So irrespective of whether you have a bad or good sequence, you will win!!!
Wait, what? So if the sequence of days is bad you will lose and then win. But if it is a good one you will win, then win, then win, then win, and finally lose. Take a peek at the pic below:


You would take it, wouldn't you? No-brainer!!!

Except that.... you will LOSE ALL YOUR MONEY IF YOU DO IT!!!!!!!!!

The program down below simulates the investment, and for some reason which I haven't thought too deeply about yet, no matter what the odds are, overtime you'll lose all your money. I ran the simulation countless times and 100% of the time you'll lose all the money. Here is an example of the simulation running:


It may take many days, but 100% of the times you'll lose it all. I don't know the why, if you do, let me know, but when I just tried a simple variation of the investment rule, things turned 180 degrees. The change is simple: instead of having 4 days of wins in a row during a "good sequence", we give you one extra day of win:


Funny enough, when you do that, your odds of winning infinity amount of money becomes 100%!!! Yes, with just one more extra day of winning, YOUR MONEY WILL GROW INDEFINITELY!!!! All you have to do in the code below is to change the nGood variable from 4 to 5 and see the results. Here is one example of the outcome:


Intriguing isn't it? Cheers, Marcelo.

static void Main(string[] args)
{
double amount = 20000;

Random rd = new Random();

bool goodSequence = rd.Next(0, 2) == 0;
int numberDays = 0;
int nGood = 4; //LOSE 100%
//int nGood = 5; //WIN 100%
for (int i = 0; i < 100000; i++)
{
int rate = 0; 

double delta = 0;
if (goodSequence)
{
for (int j = 0; j < nGood; j++)
{
rate = rd.Next(0, 100);
delta = (rate / 100.0) * amount;
amount += delta;
numberDays++;
}

rate = rd.Next(0, 100);
delta = (rate / 100.0) * amount;
amount -= delta;
numberDays++;
}
else
{
rate = rd.Next(0, 100);
delta = (rate / 100.0) * amount;
amount -= delta;
numberDays++;

rate = rd.Next(0, 100);
delta = (rate / 100.0) * amount;
amount += delta;
numberDays++;
}
goodSequence = rd.Next(0, 2) == 0;

Console.WriteLine("New amount after {0} days: {1}", numberDays, amount);
if (amount < 0.01)
{
Console.WriteLine("Lost everything after {0} days!", numberDays);
break;
}
else if (amount.Equals(Double.NaN))
{
Console.WriteLine("You became a billionaire after {0} days!", numberDays);
break;
}
}
}

Comments

  1. Fun explanation by my best friend Alexandre Coelho:

    Overall Probability = (W*W*W*W*L)/2 * (L*W)/2
    W = 1.495
    L = 0.495
    Hence overall probability = 0.92416852
    If you change the Overall Probability to (W*W*W*W*W*L)/2 * (L*W)/2, you get 1.38163194

    In other words, in the first case your overall probability is less than 1 (hence you'll lose), whereas in the second case it is greater than 1 (win)

    ReplyDelete

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