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

Home > Just Math
Permutations and Remainders (Posted on 2024-05-17) Difficulty: 3 of 5
Determine all the numbers formed by three different and non-zero digits, such that the six numbers obtained by permuting these digits leaves the same remainder after the division by 4.

No Solution Yet Submitted by Danish Ahmed Khan    
No Rating

Comments: ( Back to comment list | You must be logged in to post comments.)
Solution Analytic solution with program confirmation | Comment 3 of 4 |
All 3 digits must have the same parity, so the odd digits can be analyzed separately from the even digits.

The mod4 value of a 3-digit number is the same as the mod4 value of the last 2 digits.  

Evens: Consider flipping the last 2 digits.  What pairs of even digits have the same mod4 value when reversed?  26, 48 (or 04, but zero is excluded).  The 2 digits must differ by 4, so the only triplet would be {0,4,8} but zero is excluded.  So there is no solution with even digits.

Odds:  if both digits of a 2-digit number are odd, which ones do not have their mod4 value changed by reversing the digits?  15, 19, 37, 59  Again, the difference must be 4 (or a multiple of 4).
The only triplet which can be formed from these pairs is:  {1,5,9}.

Confirmed with a short program.
('1', '5', '9')
159 3
195 3
519 3
591 3
915 3
951 3

------------
from itertools import combinations
from itertools import permutations

for comb in combinations('123456789', 3):
    remainder = int(''.join(comb)) % 4
    winner = True
    for perm in permutations(comb):
        x = int(''.join(perm))
        if x % 4 != remainder:
            winner = False
            break
    if winner:
        print(comb)
        for perm in permutations(comb):
            x = int(''.join(perm))
            print(x, x%4)

  Posted by Larry on 2024-05-17 13:23:55
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 (0)
Unsolved Problems
Top Rated Problems
This month's top
Most Commented On

Chatterbox:
Copyright © 2002 - 2024 by Animus Pactum Consulting. All rights reserved. Privacy Information