Math Is Fun Forum

Maracuya

Member

Registered: 2008-02-02

Posts: 12

Divisibility - neat little puzzle

I came accross this on yahoo answers. :

Think your'e good at math? Try this one!?
There is a 9-digit number containing the numbers 1 through 9. Each number is only used once. This 9-digit number is divisible by 9. When you take off the right-most digit, it become an 8-digit number that is divisible by 8! When you take off the last digit to create a 7-digit number, the whole number is now divisible by 7. The pattern continues all the way down until the end, when it is a two digit number divisible by two, and then taking off the end digit creates a 1-digit number, divisible by 1.
HINTS:
*The numbers are not in order.
*Since 1+2+3+4+5+6+7+8+9=45 and 45 is divisible by 9, that clue does not help us. No matter what order the numbers are it will be divisible by 9 in the begining.
*Think about the 5th digit... what would make the number divisible by 5 when it is only 5 numbers long? There's one filled in for you!
*Review your divisibility rules.... try google to get them all. *Have fun!

Please hide your answers, or put a spoiler warning.

The original post:
http://au.answers.yahoo.com/question/index;_ylt=At1IxIq7qIPgYbcEur9WwcTg5gt.;_ylv=3?qid=20080709080930AAVi93f&show=7#profile-info-8BpETSE3aa

Last edited by Maracuya (2008-07-10 05:27:31)

mathsyperson

Moderator

Registered: 2005-06-22

Posts: 4,900

Re: Divisibility - neat little puzzle

Nice puzzle!
I won't put workings, since someone on your link has already said pretty much the same method I used, but

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Why did the vector cross the road?
It wanted to be normal.

mob_mor

Member

Registered: 2008-07-13

Posts: 0

Re: Divisibility - neat little puzzle

thank you