Given: Price at which stone was bought = Rs. 1600
Money spent on making ring of the stone = Rs. 2400
Discount offered = 10%
Marked Price = Rs. 7800
Formula Used: Profit = Selling Price - Cost Price
Calculation: According to the question
Cost price = Rs. (1600 + 2400) = Rs. 4000
Marked price = Rs. 7800
Discount = 10%
⇒ Selling price = 7800 – 0.10 × 7800
⇒ 7800 – 780 = Rs. 7020
Now, Profit = Selling price – Cost price
⇒ Rs. 7020 – Rs. 4000 = Rs. 3020
Now, Per cent profit = (Profit/Cost price) × 100%
⇒()×100 ⇒ 75.5%
∴ The profit percent is 75.5%.