Meemaw gifts Sheldon $100, and he announces to Missy while sitting in front of his Tandy 1000SX Computer that he will invest it by buying 3 Shares of Radio Shack. But this episode is set in 1992 and it was not until 2000 that the name Tandy Corporation was dropped, and it became RadioShack Corporation. He couldn't have purchased shares of Radio Shack. The average price of Tandy was $29 in 1992, so he could have purchased 3 shares of Tandy and THAT would have been a good investment because it ended the year 1993 up 63% at $49.50. Sheldon would also have needed to prove, with written documentation, that he was 18 years old to buy stock back then.