Unitary Method

Suppose 1 chocolate costs Rs 100

How much would 5 chocolate cost?

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?

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?

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?

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

= 1/6 × 54 hours

= 9 hours