[Guest]

I have tried my hardest to search this forum for the answer but I can't find it!

A friend of mine is driving me crazy with a brain teaser. He asked me to multiply random unit numbers together until i got to a nine digit number, he then told me to remove one number, then within seconds he told me what that missing number was. I thought it was something to do with the number 9, but i'm told told not. The only clue he has given me is PI !!!!!!!! This has now been driving me nuts for about two months.

He also said it works if you have an 8 digit number!

Any help on how he does this would be gratefully received!

Many thanks in advance!

Kate

[Thalia]

Did your friend pick the numbers or did you pick them?

[Guest]

i got to pick them!

[Thalia]

It actually does have to do with 9s. He is depending on you picking a 9 as one of your numbers or some 3s and 6s. Your 9 digit number will be a multiple of 9. When you took out your number and gave him the rest of the numbers, all he had to do was subtract the sum of those numbers from the next multiple of 9. So if your 9 digit number was 489888000, and you take out the 4, the total of what you give him is 41. The next multiple of 9 is 45. 45-41=4. If you pick one of the 0s, your friend has a problem though because he wouldn't be able to tell if you took out a 0 or a 9.

It was a trick performed on Pi Day.

Edited November 12, 2011 by Thalia

[Guest]

so him saying it has something to do with Pi is him just throwing me off the scent?

[Thalia]

It does have to do with pi in that it was a trick performed on Pi Day. It doesn't actually have anything to do with how he is doing it.

[Guest]

i can't get it to work, if the sum of the numbers come to 38 do i take that away from 45?

[Guest]

425689723 take the 8 out leaves 4+2+5+6+9+7+2+3 = 38 Next multiple of 9 is 45 but 45-38 is 7 ???

[Thalia]

Did you multiply numbers or did you just come up with a 9 digit number?

Your numbers add up to 46 meaning you didn't multiply by 9 or 6 and 3 at any time.

[Guest]

It was me! I really shouldn't tackle these problems after having a couple of glasses of wine! Thank you so much for your help! I am going to kill him when i speak to him next! Totally was throwing me with the Pi statement! lol!

We are currently having a discussion about BODMAS we were set the question of 5+5+5-5+5+5-5x0 which i say is 15 because of using BODMAS - i am right aren't i?

[Thalia]

We are currently having a discussion about BODMAS we were set the question of 5+5+5-5+5+5-5x0 which i say is 15 because of using BODMAS - i am right aren't i?

Is BODMAS the order of operations? Sorry. I'm used to hearing PEMDAS.

5+5+5-5+5+5-5x0

There are no parenthesis or exponents so multiplication and division are first.

5+5+5-5+5+5-0

That leaves addition and subtraction

15-5+10=20 Close but not quite.

[Guest]

... use order of operations. 5 + 5 + 5 - 5 + 5 + 5 - 5 * 0 = x

multiplication and division first, in a left to right pattern

5 + 5 + 5 - 5 + 5 + 5 - 0 = x

add and subtract like terms

15 - 5 + 10 - 0 = x

10 + 10 - 0 = x

20 = x

Unless I'm missing something and need to re-take basic algebra, the answer is 20.

Edited November 13, 2011 by Darth Legion

[Guest]

Okay now i'm not sure whether he is pulling my leg or not but he says that i'm wrong and that he would be able to guess the missing number even if i used multiples of 2 4 5 7 8 so how would that work?

He also said there is another trick using 7's?

Any help gratefully received.

Kate

[Guest]

Is BODMAS the order of operations? Sorry. I'm used to hearing PEMDAS.

5+5+5-5+5+5-5x0

There are no parenthesis or exponents so multiplication and division are first.

5+5+5-5+5+5-0

That leaves addition and subtraction

15-5+10=20 Close but not quite.

sorry i had written the sum down wrong it should've read

5 + 5 + 5 - 5 + 5 + 5 - 5 + 5 x 0 = ?

[MissKitten]

No, that still makes 15.... The 5*0 cancels it out to 0, leaving the rest to equal 15.

[Guest]

Going back to my original post - i gave him the following numbers 55073176 (one number has been removed, this was originally a 9 digit number) and he still got the missing number, i purposely did not include numbers 3 6 or 9 when arriving at this number, so he hasn't used the Pi day trick!

Confused!

[Thalia]

According to your revised equation, 15 is correct.

As for the number trick, . I'll think about it some more.

[Guest]

Maybe look for a common recurring number?