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Harvard-MIT Mathematics Tournament

Algebra Difficulty 4.3 AIME Find the answer United States

Problem:

$r$ and $s$ are integers such that
$3 r \geq 2 s - 3 \text{ and } 4 s \geq r + 12.$
What is the smallest possible value of $r / s$ ?

Your answer

A number or a short expression. Fractions can be typed as 3/2, and spacing doesn't matter.

Solution

Solution:

We simply plot the two inequalities in the $s r$ -plane and find the lattice point satisfying both inequalities such that the slope from it to the origin is as low as possible. We find that this point is $(2,4)$ (or $(3,6)$ ), as circled in the figure, so the answer is $2 / 4 = 1 / 2$ .

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Source: MathNet, licensed CC-BY-4.0. Statement reproduced verbatim; metadata (topic, difficulty) added by this project.