Final answer:
To find the original price of the watch after a 20% discount, divide the discounted price by 1 minus the discount percentage.
Step-by-step explanation:
To find the original price of the watch, we can use the formula:
Original Price = Discounted Price / (1 - Discount Percentage)
In this case, Peter received $21.00 after a discount of 20%. So, the discounted price is $21.00 and the discount percentage is 20%. Plugging these values into the formula, we have:
Original Price = $21.00 / (1 - 0.20)
Original Price = $21.00 / 0.80
Original Price = $26.25
Therefore, the original price of the watch was $26.25.