Unitary means “of one” . Mathematically it means “1”. To know this in an easy way, I am writing few examples.

Question 2: If the cost of 50 pencils is Rs 500. oo . Find the cost of One pencil .

I am modifying the above Sum a little bit .

Question 3: If the cost of 50 pencils is Rs 500.00 . Find the cost of 12 pencil .

Now the basic rule is :

For question 1. If we know the cost or other parameter of one thing , then to know the cost of many thing we will do multiplication .

Here we know the cost of 1 pen . Therefore the cost of 25 pen will be MORE than the cost of 1 one pen.

Here we realize for more value . Therefore we will multiply.

Also watch the image cost of ONE to cost of MANY means MULTIPLY.

Solution 1:

∵ the cost of 1 pen is Rs. 2

∴ the cost of 25 pens is 2×25 [we realize for more value.]

= Rs. 50

For question 2. And if we know the cost of many things or other Parameter , then to know the cost of one thing we will do division.

Here we know the cost of many pencils and we want to know the cost of 1 pencil.

We realise that the cost of 1 pencil will less than the cost of 50 pencils.

Therefore we realise for less value. Therefore we will divide.

Solution 2:

∵ the cost of 50 pencils is Rs. 500

∴ the cost of 1 pencil is 500/25 [we realize for less value. Therefore divide]

= Rs. 20

### 3rd sum is the combination of two sums. In this sum we will realise both division and multiplication.

Solution 3:

∵ the cost of 50 pencils is Rs. 500

∴ the cost of 1 pencil is 500/25 [we realize for less value. Therefore divide]

= Rs. 20

∴ the cost of 12 pencils is 20×12 [we realize for more value.Therefore multiply.]

= Rs. 240

Now watch this video.