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Judy G. Russell
June 29th, 2006, 10:26 AM
The Magic Gopher (http://www.learnenglish.org.uk/games/magic-gopher-central.swf) can read your mind...

sidney
June 30th, 2006, 08:30 AM
The Magic Gopher (http://www.learnenglish.org.uk/games/magic-gopher-central.swf) can read your mind...

Would you like to know how it works? :)

Judy G. Russell
June 30th, 2006, 10:33 AM
Would you like to know how it works? :)Yes, and of all the people on this forum, you're the one I expected would know!!!

PeteHall
June 30th, 2006, 03:30 PM
- Pick your 2 digit number 'ab'
- add the digits
a+b
- subtract them from the number you first thought of
(10a+b) - (a+b) = 9a
Hey presto, every 9th symbol in the chart is coincidentally identical and you will always hit one of them because your final answer will always be a multiple of 9

(first time I saw something like that I could see there was an 'every 9th' pattern but needed someone else to point out the simple maths)

Dan in Saint Louis
June 30th, 2006, 04:35 PM
There is a similar game:

1) Pick a 3-digit number

2) Reverse the digits

3) Subtract the smaller from the larger

4) If there is more than one digit in the result, add the digits

5) Repeat step 4) until you have a single-digit result

6) It will be "9"

Judy G. Russell
June 30th, 2006, 04:42 PM
I think what makes you crazy in this thing is the "try again" feature. Of course, the image must be changed for the subsequent try, but that's enough to make you sit there and say, "Huh??? How dey do dat???"

sidney
June 30th, 2006, 06:16 PM
Pete got the answer for this case. More generally, the process of adding the digits of a number and continuing to add the digits of the sum until you get one digit is called "casting out nines". It gives the same result whether you add the digits again whenever you get two digits in the sum, or if you add them all up and then repeat. E.g., 374 => 3 + 7 = 10, 1 + 0 = 1, 1 + 4 = 5; or 374 => 3 + 7 + 4 = 14, 1 + 4 = 5.

In any case, the single digit result is always the remainder when the original number is divided by 9. Subtracting that remainder from the original number always results in a multiple of 9.

There's a practical use for casting out nines. You can use it to check your math when you are doing arithmetic. For example, you multiply two large numbers A x B and get C. In your head add up the digits of A, adding the digits of the sum together each time you get to two digits, and call the result ing single digit 'a'. Do the same for B to get 'b'. And the same for C to get 'c'. Now multiply a times b, add its digits together if there is more than one and the result should be 'c' if you haven't made a mistake in your multiplication. It won't detect a mistake that puts you off by a multiple of nine, but it is a good quick check.

-- sidney

Lindsey
June 30th, 2006, 09:51 PM
Yes, and of all the people on this forum, you're the one I expected would know!!!
Pffffft! I'd have posted the same answer Pete came up with if I'd had the time. As it was, I wanted to get to the FHC in time to do a little more work on the film I've rented, especially since they're going to be closed until July10th for (a) a long July 4 holiday; and (b) air conditioning repair. But I was too late, alas; even though there was another hour and a half until closing time, they had decided that nobody was coming, and the staff decided to get an early start on covering everything with plastic. :(

So I'll have to wait until after July 10 to find out what happened to Mrs. Burdett, who had been summoned before the Presbytery for absenting herself from church and "violating her covenant engagement". Oh the suspense... :p

--Lindsey

Lindsey
June 30th, 2006, 10:04 PM
There's a practical use for casting out nines. You can use it to check your math when you are doing arithmetic.
Once upon a time they used to teach things like that in school. My grandfather at one time worked as a bookkeeper; people who worked with him have told me that when they were having difficulty balancing their work, he could run his finger down a column of numbers, and by the time he got to the bottom, point and say, "There's your outage right there." They also tell me he never trusted adding machines. ;)

In my early days of working in Data Processing in the S&L where I'm now employed, it was up to the operations staff to be sure that the loan payments balanced properly (since in those days, we had keypunch operators to key the payments from the loan coupons -- we had to verify that what was punched matched what the loan payment clerk had deposited.). One of the rules of thumb we went by was: if the amount you are out is a multiple of 9, look for a transposition error.

--Lindsey