2024. PROOF WITHOUT WORDS: $a, b, c, d>0$; $ \frac{a}{b}=\frac{c}{d} \Rightarrow \frac{a}{b}=\frac{c}{d}=\frac{s a+t c}{s b+t d} $. Far East Journal of Mathematical Education. 26, 2 (Aug. 2024), 71–77. DOI:https://doi.org/10.17654/0973563124008.