Hint: Assume a variable x which will represent the cost price of a single ball. Since 17 balls were sold, the cost price of these 17 balls will be 17x. The loss will be given by subtracting the selling price of 17 balls from the cost price of 17 balls. This loss is equal to the cost price of 5 balls i.e. 5x. Using this, we can form an equation in x which can be solved to find the value of x.
Complete step-by-step answer:
Before proceeding with the question, we must know the formula that will be required to solve this question.
If it is given that a product is sold at a loss, then this loss can be found by subtracting the selling price of the product from the cost price of the product . . . . . . . . . (1).
In the question, it is given that on selling 17 balls at Rs 720, there is a loss that is equal to the cost price of 5 balls. We are required to find the cost price of a single ball. Let us assume that the cost price of a single ball is x. So, the cost price of the 17 balls will be 17x. Since the selling price is Rs 720, using formula (1), the loss is equal to,
17x – 720
It is given in the question that this loss is equal to the cost price of 5 balls i.e. 5x. So, we can say,
17x – 720 = 5x
$\Rightarrow $ 12x = 720
$\Rightarrow $ x = 60
Hence, the cost price of a single ball is Rs 60.
Note: This is an easy question which can be done using basic knowledge of profit and loss. So, the only possibility of mistake is the calculation. So, one must be careful while doing calculations in such types of questions.