CBSE Class 7 Mathematics – 8. Ratio and Propartion (Notes)

Revision Notes on Comparing Quantities

Learning Goal

1. Ratio and it’s part
2. Equivalent ratio
3. Compare of ratio (Ascending and Descending)
4. Operation of ration
5. Divide a number into given ratio
6. Ratio & Proportions
7. Ratio in real life situations

Ratios

Ratio is just like a “fraction”.

The ratio is used to compare two similar quantities in same units.

Ratio is represented by “:”, which is read as “is to”. 

Example

Write the ratio of the height of Sam to John, where Sam’s height is 175 cm and john’s height is 125 cm.

Solution

The ratio of Sam’s height to John’s height is 175: 125 = 7: 5.

We can write it in fraction as 7/5.

Equivalent Ratios

It is same as equivalent fractions.

To find equivalent ratio multiply or divide by natural number.

Example

Find the two equivalent ratios of 5: 20.

Solution

First multiply it by 2.

So the two equivalent ratios are 10:40 and 1: 4.

To compare that the two ratios are equivalent or not we need to convert them in the form of like a fraction. Like fractions are the fractions with the same denominator.

Example

Check whether the ratios 2: 3 and 3: 4 are equivalent are not?

Solution

To check, first, we need to make their denominator same.

Hence the ratio 2:3 is not equivalent to 3:4.

Proportion

If two ratios are equal than it is called proportion of each other.

How to solve proportion problems?

Example

If the cost of 8 strawberries is Rs. 64 then what will be the cost of 25 strawberries.

Solution

Using Unitary Method

Solution using proportion

Let the cost of 25 strawberries = Rs. X

Hence the cost of 25 strawberries is Rs. 200