The least numbers of those (numbers) having the same ratio measure those (numbers) having the same ratio as them an equal number of times, the greater (measuring) the greater, and the lesser the lesser.
If $\frac{\overline{CD}}{\overline{EF}}=\frac{A}{B}$ (all lengths being natural numbers) and $\frac{\overline{CD}}{\overline{EF}}$ is a reduced fraction, i.e. $\overline{CD}$ and $\overline{EF}$ are co-prime, then there exists a natural number $n$ such that $A=n\cdot \overline{CD}$ and $B=n\cdot \overline{EF}.$ In other words, the ratio $\frac AB$ can be reduced by the number $n.$
Proofs: 1
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