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A number is chosen uniformly at random from among the positive integers less than 10^8. Given that the sum of the digits of the number is 9, what is the probability that the number is prime?

 Jun 17, 2019

Best Answer 

 #1
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If the sum of the digits of a number is divisible by 9, then that number is divisible by 9.

 

And if a number is divisible by 9 then it is not prime.

 

So given that the sum of the digits is 9,  the probability that the number is prime is 0.

 Jun 17, 2019
 #1
avatar+8959 
+2
Best Answer

If the sum of the digits of a number is divisible by 9, then that number is divisible by 9.

 

And if a number is divisible by 9 then it is not prime.

 

So given that the sum of the digits is 9,  the probability that the number is prime is 0.

hectictar Jun 17, 2019

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