A dealer of scientific instruments allows 20% discount on the marked price of the instruments and still makes a profit of 25 %. If his gain over the sale of an instrument is Rs 150, find the marked price of the instrument.

Explanation

To solve the problem step by step, we will follow the given information and apply the relevant formulas.

### Step 1: Define the Variables
Let the marked price of the instrument be Rs. \( X \).

### Step 2: Calculate the Selling Price after Discount
The dealer allows a 20% discount on the marked price. Therefore, the selling price (SP) after the discount can be calculated as:
\[
...