Direct and inverse proportion class 8

Direct and inverse proportions of Class 8


The number of times one quantity contains another quantity of same kind is called the ‘RATIO’ of the two quantities. Clearly, the ratio of two quantities is equivalent to the fraction that one quantity is of the other. 

Observe carefully that the two quantities must be of the same kind. There can be a ratio between Rs. 20 and Rs. 30 but cannot be between Rs. 20 and 30 mangoes. 

Form of ratio = a → antecedent. 

or a : b b  → consequent. fractions

Ratio is not altered by multiplying or dividing both its terms by the same number. 

Thus 3 : 5 is the same as 6 : 10 and 15 : 20 is the same as 3 : 4. 


Ratio are compound when antecedent multiplied by antecedent and consequents multiplied by consequent. 

If a : b, c : d, e : f 

Then compound ratio is a x c x e/b x d x f

question 1. Find the ratio compounded if the four ratios 4 : 3, 9 : 13, 26 : 5 and 2 : 15.

Solution: The compound ratio = Direct and inverse proportion.


If a : b then a2 : b2 is duplicate ratio.

question 1. Find duplicate ratio of 4 : 3.

Solution: 42 : 32 = 16 : 9.


If a : b, then a3 : b3 is triplicate ratio. 

question 1. Find triplicate ratio of Direct and inverse proportion.

Solution:triplicate ratio


If a : b then Direct and inverse proportion is subduplicate ratio.

question 1. Find subduplicate ratio of 3 : 4 .

Solution:Direct and inverse proportion


If a : b then Direct and inverse proportion is subtriplicate. 

question 1. Find the subtriplicate of 27 : 8.

Solution:Direct and inverse proportion

NCERT solutions for class 8 Maths prepared by Physics Wallah will help you to solve your NCERT text book exercise. 

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