Math Is Fun Forum

ZHero

Real Member

Registered: 2008-06-08

Posts: 1,889

Probability.

I am interested to know that "what is the probability that a number chosen at random will have the sum of its digits divisible by 9"?

Plz help...

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If two or more thoughts intersect, there has to be a point!

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Probability.

Numerals whose sum of digits is divisible by 9 represent numbers divisible by 9 and vice versa

The set S = {9,18,27,36,45,54,...} are all divisible by 9 and the sum of their digits is divisible by 9:

Every ninth number is divisible by 9 and has the sum of the digits divisible by nine. So:

P(n | 9 and sum of the digits of n is | 9) = 1 / 9 or 8 to 1 against.

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

ZHero

Real Member

Registered: 2008-06-08

Posts: 1,889

Re: Probability.

That was easy! I was wondering about Prime numbers when a question arose in my mind... now i realize that this one was of no help.

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If two or more thoughts intersect, there has to be a point!