A proportion is two equal ratios. Cross-multiply to solve. a/b = c/d means ad = bc. 3/x = 12/20 means 3 × 20 = 12x, so x = 5. Fractions and ratios as a topic are in fractions and ratios.
Keep the pairing
Miles over hours on both sides, or students over tables on both sides. Mixing units inside one ratio is a conversion problem first, in unit conversions. Scale drawings and similar figures use the same cross-multiply, in similar triangles.
Direct variation is a proportion in function form, y = kx, in direct and inverse variation.
The bottom line
Same pairing on both sides, then cross-multiply. If the labels do not match, fix the labels before you multiply.
Start practicing
Start with a free diagnostic, then drill your weak spots with 15-question quizzes and track how you're doing across Reading, English, and Math. Compare plans whenever you're ready to go further.
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