Question

A bookseller sold a book for Rs.\[100\] and thereby gains Rs.\[20.\] Find his gain percent.
A. \[20\% \]
B. \[25\% \]
C. \[40\% \]
D. None of these

Answer 1

Hint:
To solve this question, we will first find the cost price of the book, by using the given values. Because to evaluate profit percent we will need the value of cost price. Then on applying the formula of profit percent, using cost price and profit, we will get our required answer.

Complete step by step solution:
We have been given that a bookseller sold a book for Rs.\[100\] and thereby gains Rs.\[20.\] We need to find his gain percent.
So, the given selling price of book \[ = \] Rs. \[100\]
And, the profit he gains after selling the book \[ = \] Rs. \[20\]
We know that, Cost price \[ = \] Selling Price \[ - \] Profit
On putting the values in the above formula, we get
Cost price of book \[ = \;100{\text{ }}-{\text{ }}20{\text{ }} = {\text{ }}80\]
So, the cost price of the book is Rs. 80.
Now, we know that, \[Profit{\text{ }}\% {\text{ }} = \;\dfrac{{Profit}}{{cost{\text{ }}price}} \times 100\]
On putting the values in the above formula, we get
\[ = \dfrac{{20}}{{80}} \times 100\]
\[ = 25\;\% \]
So, the profit percent or gain percent is \[25\% .\]

Thus, option (B) \[25\% ,\] is correct.

Note: Students should notice that in the solutions in the formula of profit percent, we have used the cost price, and due to this reason only we have evaluated the value of cost price first. So, always keep in mind that both profit percent and loss percent are always evaluated on cost price. Because cost price is the price at which the product is bought, so whatever profit or loss is attained, we always calculated that on cost price.