Question

If the cost of 20 pens is Rs. 180, calculate the cost of 15 pens?​

Answer 1

Answer:

Using unitary method -

Cost of 20 pens = Rs 180

Cost of 1 pen = 20

180

Cost of 15 pens = 20 × 15 = 135

180

Ans) cost of 15 pens is Rs 135.

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Answer 2

The cost of 15 pens will be ₹ 135.

Step-by-step explanation:

• Given that the cost price of 20 pens is ₹ 180.
• We need to calculate out the cost of 15 such pens.
• So, the price of a single pen will be,

$cost\hspace{0.1 cm} of\hspace{0.1 cm} a\hspace{0.1 cm} pen = \frac{cost\hspace{0.1 cm} of \hspace{0.1 cm} 20 \hspace{0.1 cm} pens}{20}$

$cost\hspace{0.1 cm} of\hspace{0.1 cm} a\hspace{0.1 cm} pen = \frac{180}{20}=9$

• So, we got the cost of a single pen is  ₹ 9.

• Now, we need to compute the cost of 12 such pens.

$cost\hspace{0.1 cm}of\hspace{0.1 cm}15\hspace{0.1 cm}pens=15\times cost\hspace{0.1 cm}of\hspace{0.1 cm}a\hspace{0.1 cm}pen$

$cost\hspace{0.1 cm}of\hspace{0.1 cm}15\hspace{0.1 cm}pens=15\times 9=135$

Thus, the total price of 15 pens will be ₹ 135.