Answer:
Buying on margin.
Explanation:
It is factor leading to the stock market crash on Black Tuesday. Buying on margin meant that people did not pay the full price of stocks. They just paid a percentage and borrowed the money to pay for the rest of the price. In the 1920s this was a common practice based on optimism, on the belief of constant growth of the stock prices in that decade. As the stock prices kept going up, it was hoped the debt would be paid in this way. So, stock prices were overvalued and they fell precipitously when the financial bubble burst.
