Grievous math error in "Fishful of Dollars!"

[on:]

In this episode Fry learned he had 93 cents in his bank account from a 1000 years ago, err, I mean 4 years ago...you know what I mean.

The teller said at 2.25% interest per year for a 1000 years is 4.3 billion dollars! But that is way off!

.93e^(.0225*1000) = $5,496,785,519

[Reply #1 on:]

Wow wow, slow that brain train...

I'll take your word for it 

[Reply #2 on:]

Oh, now don't be faceicious (sic, honest), I'm sure the teller just...rounded the number down...to the nearest 4.3 billion. 

[Reply #3 on:]

4.3....1000....2.25....carry the one....errr whatever you say    

[Reply #4 on:]

MattOSX, I wrote a QBasic program to calculate the rise of Fry's bank balance over the years, and it comes to $4.28 billion.

0.93*(1.0225^1000) = 4.28 billion.

In addition, there's a logical flaw in the calculation from your first post.  I used that method and got a figure of .1953738

[Reply #5 on:]

There is no flaw in my math. Your math is wrong, the interest stated is 2.25% annually, not 1.0225% as you state.

The equation I use is a fairly common one.

sum = yo*e^kt

sum is the final figure amount
yo is the initial investment
k is the interest rate
t is time

[Reply #6 on:]

No, MattOSX.

Your math is wrong. PCC is correct. The reason he uses 1.0225 is because multiplaying with that figure is the same as adding 2.25%.

[Reply #7 on:]

If you're increasing interest then you multiply by the figure:
1 + (increase in interest as percentage)/100
^That's probably not the way to describe it, but it's right!

I.E. It's:
0.93*(1.0225^1000) not 0.93*(0.0225^100)
And i get $4,283,508,449.71

[Reply #8 on:]

@MattOSX: you're using the formula assuming it's compunded continuously. It's actually not supposed to be continuous, so "e" shouldn't even be in your equation, and PCC and 'slate and 'capto are right.

[Reply #9 on:]

 

Originally posted by MattOSX:
There is no flaw in my math. Your math is wrong, the interest stated is 2.25% annually, not 1.0225% as you state.

Hmm, let's look in my UNIVERSITY TEXTBOOK!!!

S=P(1+r/100)^n

where S= final sum, P= principal (original sum of money), r= rate of interest, and n= years.

In this case, P=0.93, r=2.25 and n=1000.

0.93*(1+2.25/100)^1000

= 0.93*(1.0225)^1000

= 4,283,508,450, or $4.28 billion.

I remember that lecture well, because a HOT blonde was sitting next to me.  What an hour that was! 

[Reply #10 on:]

Ahhhh! I'm truly sorry, Fred. I totally forgot it was a discrete kind of math. I just built my own realbasic app to check and sure enough, it is 4.28 billion.

Sorry 

Atleast I now have a handy interest app handy 

[Reply #11 on:]

No probs. Athough I'm jealous that you have better Basic software than me... 

Besides, thinking about that blonde's cheered me up for no reason... 

[Reply #12 on:]

 

Originally posted by PCC Fred:
I remember that lecture well, because a HOT blonde was sitting next to me.  What an hour that was!

The fact that you actually paid attention to the lecture indicates to me that said HOT blonde is a dirty, dirty lie.

Either that or you're gay.

Anyway, I think we learned an important lesson about questioning the math of people who have degrees in various math-related fields.