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MagnusMagus, believe it or not, but the Windows (at least XP) calculator in scientific mode can calculate lg!

 

Dont tell me you did some nifty trick with calc for my H-thingie.. you supposed to calculate it with your gray cells!! Ah well, the youth will always get lazier

 

Once i got funny lim joke, but i lost it so i will try t reconstruct it:

lim 3 = 8
w->oo

It is better when you write it in different font or when it is handwritten.

And while searching for that one i found this one that was similar:

The limit as n goes to infinity of sin(x)/n is 6.

Proof: cancel the n in the numerator and denominator.

[ December 22, 2002, 23:17: Message edited by: ToTaL ]

 

Tried that, but it doesn`t use it the same way i`m used to.
Basically, i`ve got no idea how to use Win Calculator for anything more than what I do in my head anyway

[ December 22, 2002, 23:31: Message edited by: MagnusMagus ]

 

ToTal, I don't get your "lim joke". Could you please explain it to me? The limes of 3 is 8 when w grows to infinity?! [Please excuse bad mathematical terms]

 

I get ToTal's first lim joke. I think it has something to do with writing a 3 and a backwards 3 together to get 8. And then w and an upside-down w to get oo (infinity).

Here's a similar lim joke:

lim 8 -> oo so lim 3 -> w

because you just rotate the number 90 degrees clockwise.

 

Lacking the time to read every response, I hope these have not been posted yet. There is SohCahToa in reference to tangent sine and cosine, and what they are made up of.
Why six afraid of seven? Because seven eight nine.
What did the constipated mathematician do? He worked it out with a pencil.
What did the constipated accountant do? He worked it out on a calculator.

 

OK, got it.

 

Do you remember those "magic tricks" where you pick a number, do a whole bunch of mathematical operations on it, and it ALWAYS ends up equal to a certain number?

I'm wondering if anyone knows how to derive them; it'd be nice to prove that it is a consequence of math more than magic.

 

Here's a well-known card trick that heavily relies on math. Did this one a lot when I was a kid.

Make a deck of 21 cards out of a full deck and move the extra cards away. Don't count aloud.
Now let your friend pick a card out of the deck, memorize it, and put it back in the deck wherever they want.
Shuffle the deck. Let them shuffle it if they want.

Now repeat the following procedure 3 times:
a) Ask your friend to watch out for his card, but not say anything until you're finished.
b) Distribute the deck into 3 heaps, cards facing upwards, going always from left to right: left-middle-right-left-middle-right-... When you have all the 21 cards in the 3 heaps, ask them which heap their card is in.
c) Regroup the 3 heaps into one deck, making sure that the deck they pointed out is the middle one (important!) without letting them notice that you're always putting their heap in the middle (talk about something to distract their attention - this is where the arty part is - use both hands to pick up the heaps). So, for example, if the card is in the left heap, regroup the deck such that the left heap is surrounded by the middle and right heaps.

Without reshuffling the cards, repeat the above 2 more times (3 times total).

When you're done, casually take the deck and open the cards one by one. Pretend to think once in a while, or hesitate on seeing a card, but count the cards you're opening. The card your friend chose is always the 11th card. At the 11th card, stop and say "Is this it?", with a big grin on your face.

Explanation:
What the 3 heaps distribution/reorganisation does is put the chosen card *exactly* in the middle of the 21-card deck - the 11th card.

 

Choose a number from 1 to 10 inclusive.
Multiply by 9.
Add the digits together.
If you`re left with a two digit number, add the digits again.
Subtract 5.
Find the corresponding letter of the alphabet, where 1 is a, 2 is b, etc.
Think of a country who`s name in English starts with that letter.
Think of the last letter of that country.
Think of an animal starting with that letter (types of animals - dog, cat, et al; not specific animals - Fido, Puss ).
Think of the last letter of that animal.
Think of a fruit starting with that letter.

Denmark - Kangaroo - Orange ??

How it works:
You multiply by 9. In multiples of nine , the digits always add to give 9 or a multiple of 9.
If it`s 1 - 10, x 9 will give one of:
09, 18, 27, 36, 45, 54, 63, 81, 90
Adding the digits in all of them:
9, 9, 9, 9, 9, 9, 9, 9, 9, 9 (the line about a two-digit number is put in there to throw you off)
9 - 5 = 4
4 = D
Most people think then of either "Denmark" or "Deutsland" - saying English name rules out Deutsland.
Last letter is then K - animals starting with k:
Kestral
Kingfisher
Kookaburra
Koala (NOTE: there is no such thing as a Koala Bear)
Kangaroo
Killer Whale

Most people will either not think of either of the first 3 as "Animals" (they`re birds), or they`ve never heard of them.
Can you name a fruit starting with 'E' ??
Thought not.
Leaving Kangaroo and Koala. Most people (98%) think of Kangaroo. Fruit starting with O - Onion isn`t a fruit, leaving "Orange".

 

But it can also be:

Dominican Republic - Cat - Tart with a cherry
or
Dominican Republic - Civet - Tart with a strawberry
or
Dominican Republic - Crocodile - EGGPLANT???
or
Dominican Republic - Crane - EGGPLANT!?!? again
or
Dominican Republic - Clown Fish - Heggplant!!!
or
Dominican Republic - Chamelleon - Duh... Nuts!?

...just kidding. I have used that math riddle a number of times and once in a while somebody (in their complete innocence) comes up with answers that either makes you laugh or leave you stumpped. A tomato may be an answer... but not every nation considers it as a fruit, like here, it's a vegetable. So is eggplant.

PS. Once an Englishman gave me "Dutch" as his country!

How about this one:
Prove me right or prove me wrong but you can never get the exact value of the area of a circle.

[ December 26, 2002, 09:03: Message edited by: nior ]

 

Yes you can. The hard part is getting an exact value for the diameter, but it *is* possible.
Once you`ve got an exact value, we`ll call it d, half it; d/2, and multiply by pi squared.
Here you mention the irrationality of pi, and I say that pi is an exact value - pi cannot just be *anything*, it represents and exact number.
Therefore, leaving an equation as, say (4pi)^2 means an exact value, not just 'the square of four times a number'.

 

> I'm wondering if anyone knows how to derive
> them; it'd be nice to prove that it is a
> consequence of math more than magic.

These mathemagical chains often rely on the fact that multiplying a number with "9" and adding the digits of the resulting number up and adding the digits of THAT number up again and so on until you have only one digit left - it always becomes a "9", too!

Examples:
8*9=72 -> 7+2=9
44*9=396 -> 3+9+6=18 -> 1+8=9

 

Wow, I've never noticed that multiplying by 9 sets up the digits of the number so nicely! That's some neat stuff!

 

That's a cool one Maertyn!

MagnusMagus, that's a good one... but that is theoretically. In reality we have yet to know the exact value of Pi. So I guess it's "it can" and "it can't".

 

There is indeed a fruit that starts with E. Elderberry. And yes, it is a fruit.

 

Trying explaining why this one works:

1) Pick three numbers between 1 and 9 inclusive.
2) Find their sum.
3) With those three numbers again, eliminate one of them.
4) With the remaining two numbers, form a new number. (Eg: if 1 and 2 left, can make 12 or 21)
5) Subtract step 2 from step 4. ie: the new number minus the sum of the three original numbers.
6) Reveal your answer to the 'magician'.

Now the 'magician' does some mental math:

How far is the nearest multiple of nine from that revealed number? That is the eliminated number (from step 3)!! Of course, put on a big grin

I can use algebra to show that it works, but I don't really know why.
ie: Why was the nearest multiple of nine used? (I have a feeling that the trick with the 9 posted above is somehow involved)

 

Barney = Satan
The truth is finally known! Barney seems innocent and sweet but in fact he is Satan. It's all very simple:

1) Start with the given: CUTE PURPLE DINOSAUR
2) Change all U's to V's (which is proper Latin anyway): CVTE PVRPLE DINOSAVR

3) Extract all Roman Numerals: C V V L D I V

4) Convert into Arabic values: 100 5 5 50 500 1 5

5) Add all the numbers: 666

Thus, Barney is Satan.

 

Wouldn´t that make the cute purple dinosaur Satan??