Explanation:
Let's assume the buying rate of each book is x dollars.
The bookseller bought 120 books at a sum of money, so the total cost price (CP) of the books is 120x dollars.
The bookseller sold 80 books at $90 each, so the revenue from selling those books is 80 * $90 = $7200.
The remaining books, which is 120 - 80 = 40 books, were sold at $60 each, so the revenue from selling those books is 40 * $60 = $2400.
The total revenue from selling all the books is $7200 + $2400 = $9600.
We are given that there is a loss of 20% on the total sale. Loss percentage is calculated based on the cost price. The loss is equal to 20% of the cost price, which is (20/100) * 120x = 24x dollars.
We can equate the loss to the difference between the cost price and the total revenue:
24x = 120x - $9600
Simplifying the equation, we get:
120x - 24x = $9600
96x = $9600
Dividing both sides by 96, we find:
x = $100
Therefore, the buying rate of each book is $100.