Elementary proof: division by integer makes real number smaller.

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It's been so long since I took discrete math, maybe someone here can help me with what ought to be a straight forward and simple proof.

Effectively I want to show this:

  • Let a and b be positive integers where b>a and b != 0. (a/b is a rational number between 0 and 1, non-inclusive).
  • Let k and l be (real?) numbers where k = l(a/b)
  • (Meat of the proof here)
  • Then for any l, k < l.

My discrete book doesn't really get into quite this case, and I don't really know what to search for here to find this type of proof. Thanks!

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First of all you need $l>0$ to have the result.

$$l-k=l-l\frac{a}b=l\frac{b-a}b>0$$ as $l$ and $\frac{b-a}b$ are both positive. So, $l>k$.