Prove that every integer n>= 14 is a sum of 3's and/ or 8's.

In summary, the task is to prove that for any integer n >= 14, there exist non-negative integers a and b such that n = 3a + 8b. This can be done by first considering multiples of 3 and showing that a non-negative solution can be found for each n, and then considering the two adjacent integers to show that the property holds for all integers >= 14. Induction may not be the most suitable approach for this proof.
  • #1
snaidu228
9
0

Homework Statement



Prove that every integer n>= 14 is a sum of 3's and/ or 8's.

Homework Equations



Induction Hypothesis

The Attempt at a Solution



Base Case: P(0):

Suppose n= 14, and k is an integer representing number of times 3 or 8 is added:
14= 3k;
k=14/3 ( this shows that 14 is not a sum of 3's)

But the question says to show that. I'm confused on how to show that.
 
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  • #2
14= 3+3+8
it's and/or
 
  • #3
You need to be able to show that every number >= 14 is a linear combination of 3s and 8s. IOW, that n = 3a + 8b for some integer values of a and b, with a >= 0, b >= 0. (I don't think that either a or b can be negative, but either one could be zero.)

That's what you need to show, but I don't have any idea right now of how to go about doing this.
 
  • #4
Mark44 said:
IOW, that n = 3a + 8b for some integer values of a and b, with a >= 0, b >= 0. (I don't think that either a or b can be negative, but either one could be zero.)
That parenthetical remark is essential. Consider n=13. This has solutions for a,b in the integers. For example, a,b = -1,2 and 7,-1 are both solutions to 3a+8b=13. In fact, given any integer n, there are an infinite number of solutions a,b in Z such that 3a+8b=n. So the problem is to not only show that integer solutions a,b exist but also to show that at least one such solution has both a and b non-negative.
 
  • #5
BTW, induction might not be the best choice here. Start with multiples of 3, n=3m. This obviously has a,b=m,0 as one solution to 3a+8b=n, and this a,b is in the non-negative integers if n is non-negative. What can you say about the two adjacent integers, n-1 and n+1?
 

FAQ: Prove that every integer n>= 14 is a sum of 3's and/ or 8's.

1.

What is the problem statement?

The problem statement is to prove that every integer n greater than or equal to 14 can be expressed as a sum of 3's and/or 8's.

2.

Why is this problem important?

This problem is important because it demonstrates the concept of integer compositions and can have real-world applications in areas such as computer science and number theory.

3.

What is the significance of the number 14 in this problem?

The number 14 is significant because it is the first integer that requires both 3's and 8's to form a sum. It serves as a starting point for the proof.

4.

What is the approach to proving this statement?

The approach to proving this statement is by using mathematical induction. This involves proving a base case (n=14) and then proving that if the statement holds for n=k, it also holds for n=k+1.

5.

Can you explain the concept of integer compositions?

Integer compositions are ways of expressing an integer as a sum of smaller positive integers. For example, the integer 10 can be composed as 5+3+2, 4+4+2, or 3+3+3+1. This concept is important in this problem because we are trying to show that every integer n>=14 can be composed using only 3's and/or 8's.

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