Question

10. If 15 postcards costs 7.50. What will be the cost
of 36 such postcards ? Also find the number of
postcards one can buy for $45.​

Answer 1

Answer :-

• The cost of 36 postcards = $ 18.

• 90 postcards can be bought by a person for $ 45.

Given :-

• 15 postcards cost 7.50.

To find :-

• The cost of 36 such postcards.

• The number of postcards one can buy for $ 45.

Step-by-step explanation :-

Detailed explanation of the solution :-

Let's understand!

• This question has been divided into two parts. In the first part, we have to find the cost of 36 postcards when 15 postcards cost dollar 7.50 and in the second part, we have to find the number of postcards one can buy for dollar 45.

• For the first part, we are going to use Unitary Method and find the cost of 1 postcard by dividing and then use it to find the cost of 36 postcards by multiplying.

• And in the second part, we are first going to use Unitary Method and find the number of postcards one can buy for dollar 1 and then find the number of postcards one can buy for dollar 45.

Let's calculate now!

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Calculations :-

First part :-

Cost of 15 postcards = $ 7.50

Therefore, cost of 1 postcard =

$\sf \dfrac{7.50}{15} = 0.50$

Now, in decimals there's no value of the extra zeroes at the end of the number. So, let's remove the extra zero from 0.50 and make it 0.5.

Since the cost of 1 postcard = $ 0.5,

Therefore the cost of 36 postcards =

$\sf 0.5 \times 36 = 18$

Therefore, the cost of 36 postcards is $ 18.

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Calculations :-

Second part :-

Cost of 15 postcards = $ 7.50.

So, that means the number of postcards which can be bought for $ 7.50.

Hence the number of postcards which

can be bought for $ 1 = $\sf\dfrac{15}{7.50} = 2$

Since 2 postcards can be bought for $ 1,

Therefore, the number of postcards that can be bought for $ 45 = $\sf2 \times 45 = 90$

Thus, 90 postcards can be bought for $ 45.

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