How should I solve this Diophantine equation word problem?

  • Thread starter Thread starter Math100
  • Start date Start date
  • Tags Tags
    Word problem
Join the discussion
Registration is free. Ask a follow-up in this thread, or start your own.
4 replies · 2K views
Math100
Messages
823
Reaction score
234
Homework Statement
Alcuin of York, 775. One hundred bushels of grain are distributed among 100 persons in such a way that each man receives 3 bushels, each woman 2 bushels, and each child 1/2 bushel. How many men, women, and children are there?
Relevant Equations
None.
Proof: Let x be the number of men, y be the number of women
and z be the number of children.
We need to find the solutions in the non-negative integers
for the Diophantine equation 3x+2y+0.5z=100 such that
x+y+z=100.

From x+y+z=100, we have that z=100-x-y.
Substituting z=100-x-y into the Diophantine equation
3x+2y+0.5z=100 and multiplying it by 2 produces:
5x+3y=100.

Applying the Euclidean Algorithm produces:
5=1(3)+2
3=1(2)+1
2=2(1)+0.

Now we have that gcd(5, 3)=1.
Note that 1##\mid##100.
Since 1##\mid##100, it follows that the Diophantine equation
5x+3y=100 can be solved.

Then we have 1=3-1(2)
=3-1(5-1(3))
=2(3)-1(5)

And now I'm stuck on this problem. I know I need to find the x0 and y0 in order to seek the general solution of the Diophantine equation. How should I go from here?
 
Last edited by a moderator:
Physics news on Phys.org
From ##3x +2y = 100## you could do some modulo arithmetic.

PS It shold be ##5x +3y = 100##, of course!

There are lots of solutions.
 
Last edited:
But this problem is from the section of Diophantine equations. Would it still be okay to do some modulo arithmetic without doing the back substitution for the Diophantine equation 5x+3y=100?
 
Math100 said:
But this problem is from the section of Diophantine equations. Would it still be okay to do some modulo arithmetic without doing the back substitution for the Diophantine equation 5x+3y=100?
Modulo arithmetic is as Diophantine as it gets!