Ratio
- CBSE · NCERT Class 8 Part 1, Ch 7 Proportional Reasoning-1
A ratio compares two quantities of the same kind by division, written a : b, such as 3 : 2 for 3 cups of rice to 2 of dal.
A ratio tells you how much of one thing there is for each amount of another. The two numbers are the terms of the ratio. Order matters: 3 : 2 is not the same as 2 : 3.
Like a fraction, a ratio can be cut down. Divide both terms by the same number. 45 : 30 becomes 3 : 2 after dividing by 15. Both quantities must be in the same unit before you compare them.
A small example
A class has 18 girls and 12 boys. The ratio of girls to boys is 18 : 12. Divide both by 6 to get 3 : 2. So for every 3 girls there are 2 boys.
Where marks go
Question 6 of the CBSE Maths Standard sample paper for 2026-27 gives two similar triangles with perimeters 56 cm and 70 cm. One side of the first is 14 cm. It asks for the matching side of the second.
The marking scheme's solution uses one fact: the ratio of the perimeters equals the ratio of matching sides. So 56 : 70 = 14 : x, and x = 17.5 cm. It is a 1-mark multiple-choice question. Setting the ratio up the wrong way round gives a wrong value. With no part marks, the whole mark is lost.
Sources
Facts last checked against these sources on 30 September 2026.
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