Question

A diamond ring costs $1,020 to manufacture and is sold in stores for $1,275. While, a ruby ring that normally sells for $290 is on sale for $203.

Answer 1

The 2nd paragraph has the straightforward answer, technically.

This is an example of gross domestic product and today's marketing. When a product is usually paid more money to manufacture than it costs to actually sell. However, the usual difference between manufacturing cost and sales cost is on average is at most 5 - 15% of the manufacturing cost.

The second problem however is just the perfect example of sales and sales tax. The diamond ring is on sale for 30% off in this case, because 290 divided by its percent is equal to 30%, the remaining amount.