first of all i dont know second, i want to ask this question: How would you know it is a 1920 Mercury dime if the obverse was a penny? It sounds like you have a magician's coin made by cutting apart both a dime and a penny, and hollowing out one side of the penny so the dime side snaps into the penny side. It's interesting but has no value to a coin collector.
The front (obverse) of the dime pictures a left-facing profile of Franklin Delano Roosevelt.
If it looks like a Wheat cent reverse and Mercury dime obverse what you have is a magic coin used in slight of hand tricks and has no collectible value.
A 3 cent piece has III on reverse. It is the same size as a dime 17.9mm. An 1866 with a star on obverse will bring a nice amount of $$$ depending on condition.
1920 is a common date for mercury dimes. In circulated condition, your dime is worth about $2 in silver melt. In better shape it might be worth closer to $10 or even more if well struck and completely uncirculated.
Winged Liberty Head also known as Mercury Dime. The figure on the coin's obverse is often thought to be the Roman god Mercury, but is in fact a depiction of Liberty (all other dimes except the Roosevelt Dime feature an image of Liberty).
US dimes had different poses of Lady Liberty portrayed on their obverse sides from 1796 until 1945. Starting in 1946 Franklin D. Roosevelt was portrayed on the obverse of the dime and has continued to this day.
A 1920 mercury head dime is fairly common. It is 90% silver and 10% copper, with a value of $2.00 just for the silver. The collectible value is $4.00-$8.00 for an average circulated coin.
One tenth of a dime is one cent.
It is worth more because only 1,230,000 were made as opposed to 1920 (59,030,000) or 1923 (50,130,000).
If it's a U.S. dime with a date of 1944, it's a Mercury dime.
This riddle is referring to American nickels and dimes. From 1938-present the nickel has featured Thomas Jefferson on the obverse. From 1946-present the dime has featured FDR on it. So 2 nickels (American 5 cent pieces) make one dime (American 10 cent piece)
A good rule of thumb that most collector's use is to add half a cent for each year it's been in circulation. It's 2012 now, so 2012-1920= 92 years. 92 x 1/2= 46. So your 1920 dime should be worth about 56 cents.