Math wizards - what's the trick to this?

“I've seen other things like this and usually I can figure out the mathmatical trick, but not this time. Must be the early morning hour. So, what's the trick?

http://digicc.com/fido/”

“I just tried it and it was wrong.



Oops pardon me it's to early in the morning. My math was wrong. Lessee here, nope still wrong.
last edited: 10/27/05 8:23:48 AM”

“treebeast - It was giving you the number you circled, not your original number.

I can tell you the secret if you really want to know. It uses a very useful technique...I learned it in the 6th grade for checking arithmetic problem answers (yes...before we had calculators).”

“OK. A see this link about "Casting out nines"

When you subtract the rearranged number from the original one, the answer must have a "casting out of nines" equivalent of zero. So once you give the jumbled number, it just finds out what missing digit would make the total "nines" equal to zero.

Yep. Learned that in 1960.
last edited: 10/27/05 10:01:41 AM”

“Another hint please......better yet, just come out with it already! The whole trick!”

“I wanna know.

Does anyone know 'elephants in Denmark' because I used to but forgot it.”

“It has something to do with the fact that we use base-10 numbers. I would have to put more thought into it to figure out the specifics.”

“Yes WB, I know that one.

Pick a number from 1-9 and then mulitply that number by 9. Take those two digits and add them. Minus 5 from that. Take that number and transpose it to the alphabet. A==1, B=2, etc. Now, think of a country that starts with the letter you have. Now take the second letter in that country and think of an animal that starts with that letter...and remember, there are no elephants in Denmark.”

“I revised my second response within 10 minutes
from a hint to the answer.”

“I don't know about the Denmark part but the "multiply by 9" part makes it modulo 9 math.”

“It was still wrong Phil. It said I circled a 6 but I circled a 9.”

“What? I got that there are no Opossums in the Domenican Republic...”

“I always come up with "jackasses from Djibouti" with that one.”

“Simer, normally, people choose Denmark and normally, the first animal they think of that starts with an E is an elephant. There are those who don't hear country and chose Denver and then there are those who think of an emu. You are the first to come up with the Dominican Republic, though.”

“treebeast - Absolutely doesn't matter what number you start with. As long as you subtract the two numbers properly, they can always tell you any number you eliminate (circle) from the answer because the casting out of nines result will always be zero.

(I don't suppose you could have subtracted wrong?)”

“here's a good one:

think of a number less than 99,999

add up all the digits to get a number 1 - 45
multiply it by 3
subtract 78

now take that number and convert it to letters (a=1, b=2)

check out the word you just created!”

“fi”

“Ah I fatfingered entering the number. That 'splains it.”

“It didn't work if you use all the same digits like 7777. You get zero, and there is only one number to circle, yet it gave me a 9”

“The instructions say to make the number random with lots of different digits. It also says not to pick zero as the number you circle.
last edited: 10/27/05 11:48:13 AM”

“I knew someone would come through, thanks.”

“By the way, that is easily converted into a bar trick you can used to get free drinks!

I am not promoting the consumption of alcohol...but rather another side to the way you can use math and statistics to broaden your life experience.”