All about flooble | fun stuff | Get a free chatterbox | Free JavaScript | Avatars    
perplexus dot info

Home > Probability
Set of Primes (Posted on 2009-05-18) Difficulty: 2 of 5
Let X be set of primes from 1 to 100, i.e., X: {2,3,5,7,....,97} and Y be set of numbers whose every prime divisor belongs to set X. A number from Y has exactly 24 positive divisors, find the probability it has exactly 3 distinct prime divisors.

See The Solution Submitted by Praneeth    
Rating: 3.0000 (1 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
re: solution | Comment 3 of 6 |
(In reply to solution by Daniel)

Hi Daniel,

I fear you made some mistakes is your calculation.
You say that "2: is p1^2*p2^12 or p1^3*p2^8 or p1^4*p2^6 and this gives another 900 numbers". This is, however, not true.
For the first part, let's say the one with power 2, there are 25 possibilities. For the second there are 24. You seem to have divided by 2, but switching the two numbers would give a different result. Something similar happens in (3) and (4).

  Posted by Robby Goetschalckx on 2009-05-18 12:00:21

Please log in:
Login:
Password:
Remember me:
Sign up! | Forgot password


Search:
Search body:
Forums (0)
Newest Problems
Random Problem
FAQ | About This Site
Site Statistics
New Comments (7)
Unsolved Problems
Top Rated Problems
This month's top
Most Commented On

Chatterbox:
Copyright © 2002 - 2017 by Animus Pactum Consulting. All rights reserved. Privacy Information