---
source: ncert
topic: arithmetic
class_level: class_6
chapter: ch12
difficulty: beginner
---

Class 6 | Ch12: Ratio and Proportion
Ratio a:b = a/b. No units. Both quantities must be in SAME unit first.
Equivalent: 2:3=4:6=6:9.
Proportion a:b::c:d: product of extremes = product of means: a×d=b×c.
Unitary method: find cost of 1, multiply for required number.
Example: Divide 720 in 4:5. Total parts=9. Shares: 4/9×720=320 and 5/9×720=400.
Proportion check 3:4 and 9:12: 3×12=36=4×9=36. YES.
6 pens cost 90 → 1 pen=15 → 10 pens=150.
50cm:2m must convert → 50:200=1:4. Ratio requires SAME units.