Question

A stationer buys 5 pens for Rs 28 and sells them at the profit of 25%. How much should a customer pay if he buys 3 pens?

Answer 1

Hint: In this question, we are given the cost price and profit percentage of the pens and we have to find the selling price of the pens. We will first use the unitary method to find the cost price of one pen and then we will use the basic cost price, selling price formula which is \[SP=CP+~profit\]where SP is selling price and CP is cost price.

Complete step by step answer:
We are given a cost price of 5 pens which is Rs 28, to simplify the sum, we will find the cost price of 1 pen by unitary method.
Cost price of \[5\text{ }pens\text{ }=\text{ }Rs\text{ }28\]
Cost price of \[1\text{ }pen\text{ }=Rs\text{ }\dfrac{28}{5}=Rs\text{ }5.60\]
As we are given the profit percentage which is 25%, we will convert it to profit to simplify calculation.
\[profit=\dfrac{profit\text{ }percentage}{100}\text{ }\times \text{ }cost\text{ }price\]
\[=\dfrac{25}{100}\text{ }\times \text{ }5.60\]
\[=1.4\]
As we know, selling price is equal to sum of cost price and profit. Hence,
\[SP=CP+~profit\]
\[SP=5.60+1.4\]
\[SP=7.00\]
Hence, the selling price of one pen is \[Rs\text{ 7}\]. But we have to find the selling price of 3 pens, so we will multiply \[Rs\text{ 7}\]by 3, and we will get \[7\times 3=21\].

Therefore, the selling price of 3 pens is Rs 21.

Note: Students should always apply formula for 1 pen product only if cost price and selling of different numbers of products is required. Students can apply direct formula for finding selling price which is,
\[SP=\left( \dfrac{100+profit\text{ }%}{100} \right)\text{ }\times \text{ CP}\]
As we found earlier, CP of one pen is Rs5.60, profit percentage is 25%
Putting values in above formula, we get
\[SP=(\dfrac{100+25}{100}\text{) }\times \text{ 5}\text{.6}\]
\[=\text{ }(\dfrac{125}{100}\text{) }\times \text{ 5}\text{.6}\]
\[=5\text{ }\times \text{ }1.4=Rs\text{ 7}\]
Hence, the selling price of one pen is \[Rs\text{ 7}\].
Selling price of three pens is \[Rs\text{ }7\text{ }\times \text{ 3}=Rs\text{ 21}\].
Also, students should not get confused with profit and profit percentage.