At an eBay auction, a woman's ring and a filigree jewelry box with a hand-painted ceramic top are on sale for $200.00 Dollars.
The jewelry box is valued at $190.00 Dollars more than the ring. How much is the ring worth?

Answer:

If you said $10.00 Dollars, you are wrong! It is not that simple.

This is a problem that requires setting up two equations with two unknowns to find the answer.

The box (B) plus the ring (R) cost $200.00 Dollars:

B + R = 200

The jewelry box is valued at $190.00 Dollars more than the ring,
i.e., the price of the box (B) is equal to the price of the ring (R) plus $190.00 Dollars:

B = R + 190

Now we can substitute the right side of the second equation in the first equation and solve for R.

R + 190 + R = 200
2 R = 200 - 190
2 R = 10 R = 10/2 R = 5

The ring is worth $5.00 Dollars.

The price of the box is $190.00 plus $5.00, which is $195.00 Dollars, and the box plus the ring add up to $200.00.
So, everything checks out.