Page 143 - Math Skill - 5

Money 141

2. Multiply the following.

(a) ` 24.45 by 16 (b) ` 198.05 by 20 (c) ` 98.89 by 35 (d) ` 410.37 by 18
3. Divide the following.

(a) ` 388.85 by 5 (b) ` 2945.70 by 9 (c) ` 283.25 by 11

Unitary Method

While shopping, we often come across such situations where we are provided with the cost of
one object and we need to buy more number of the same object.

For example, the cost of one pen is ` 25 and we need to buy four pens.
Cost of 1 pen = ` 25

Cost of 4 pens = ?

In such a case, we will multiply and find out that the cost of 4 pens will be equal to ` 100.
Cost of 1 pen = ` 25

Cost of 4 pens = ` 25 × 4 = ` 100
But sometimes, we come across such situations where we are provided with the value of some
and we need to find out the value of more items.

For example, cost of one dozen bananas is ` 24. What will be the cost of 15 bananas?
To solve problems like this, we use unitary method.

Unit means one. Unitary method is the method of calculation, when we know the value of:

™ One and need to find out the value of many.

Example 2: Divide ` 658.70 by 14. ™ Many and we need to find out value of one.

Solution: 4 7 .0 5 ™ Some and need to find out value of many.
14 6 5 8 .7 0 Case 1: Cost of one kg apples is ` 95 per kg. What will be the cost of 10 kg apples?
– 5 6 Cost of 1 kg of apples = ` 95
9 8
– 9 8 Cost of 10 kg of apples = ` 95 × 10 = ` 950
7 0 Case 2: Cost of fifteen bags of pulses is ` 1,250. What will be the cost of 1 bag of pulses?
– 7 0
× Cost of 15 bags of pulses = ` 1,250
Cost of 1 bag of pulses = ` 1,250 ÷ 15 = ` 83.33
Hence, ` 658.70 ÷ 14 = ` 47.05
Case 3: Cost of one dozen bananas is ` 48. What will be the cost of fifteen bananas?
In this case we will first find the cost of one banana and then multiply it with 15.

Cost of 12 bananas = ` 48 [ 1 dozen = 12]

So, cost of 1 banana = ` 48 ÷ 12 = ` 4
Therefore, cost of 15 bananas = ` 4 × 15 = ` 60