Suppose 1 chocolate costs Rs 100

How much would 5 chocolate cost?

18.jpg

Cost of 1 Chocolate = Rs 100

Cost of 5 Chocolate = Rs 5 × 100

= Rs 500

 

Let’s take another example

Suppose 5 pens cost Rs 100. How would 9 pen cost?

 

19.jpg

Cost of 5 pens = Rs 100

Cost of 1 pen = Rs 100/5

Cost of 9 pens = Rs 9 × 100/5

 = 9 × 20

 = Rs 180

 

So,

What we did was,

We find cost of 1 pen, & then find cost of 9 pens

 

This method of finding value of 1 unit

& then using it to find value of multiple units is called Unitary Method.

 

Let’s take another example

Three watches cost Rs 1200. How much five watches would cost?

 

13.jpg

Cost of three watches = Rs 1200

Cost of one watch = Rs 1200/3

Cost of five watches = Rs 1200/3 × 5

  = 400 × 5

  = Rs 2000

 

5 identical books weights 5 kg. How much 3 of these books weight?

 

14.jpg

 

Weight of 5 identical books = Rs 5 kg

Weight of 1 books = 5/5 kg

Weight of 1 books = 5/5 kg × 3 kg

= 1 × 3

= 3 kg

 

 

A train takes 3 hours to travel 180 km. How much time would it take to travel 540 km?

Time taken to travel 180 km = 3 hours

Time taken to travel 1 km = 3/180 hours

 

Time taken to travel 540 km = 3/180 × 540 hours

= 3/18 × 54 hours

  3/6 × 54 hours

= 9 hours

  1. Chapter 8 Class 7 Comparing Quantities
  2. Concept wise
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Davneet Singh
Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 8 years. He provides courses for Maths and Science at Teachoo. You can check his NCERT Solutions from Class 6 to 12.