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Make it solvable (Posted on 2005-05-05) Difficulty: 4 of 5
a, b, and x are positive integers such that

sqrt(a) + sqrt(b) = sqrt(x)

How many possible values of x less than or equal to 1000 are there?

See The Solution Submitted by Jer    
Rating: 3.6667 (3 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
re(2): Independent Solution | Comment 12 of 18 |
(In reply to re: Independent Solution by John Reid)

You are correct about my counting method.  I was methodically counting the numbers below 1000 that had no more than 1 of each prime in the prime factorization.  I'm glad you spotted my error.  I knew when I saw that yours differed by 1 that I probably made a counting error.  When I did so much counting by hand, I was bound to make an error somewhere.

I have since read your solution.  I think it's amazing how we came to the same conclusions and counted the same number with completely different methods!  I didn't think of using combinatorics for the counting method.  I love combinatorics, and I kept on wondering if I could use it to avoid all that tedious counting.

I think the other solutions do not agree because of a misinterpretation of the problem.  When I started reading the comments, it seemed everyone was trying to count the number of possible sums rather than the number of possible values of x.  I lost interest, and wrote my own solution instead.  I think I mentioned in my solution that counting the number of sums was a lot more difficult.

  Posted by Tristan on 2005-05-06 05:53:45

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