Whereabouts of dime with missing letter had been a mystery for decades
                                
                                
                                    (Newser) -
                                    An incredibly rare dime has sold for the equivalent of more than 5 million ordinary dimes. The coin, whose whereabouts had remained a mystery since the late 1970s, sold for $506,250 in an online auction that concluded Sunday, according to auction house GreatCollections, per the  AP . The dime is...