Sixty four thousand dollar question

This has come to mean the crucial or ultimate question that needs to be addressed in any quest or endeavour. It is usually written in number form 64,000 and derives from the US television quiz show of the 1960s where 64,000 dollars was the top prize. With inflation, 64,000 dollars is becoming a less impressive sum of money as the years go by. Therefore, not surprisingly, the expression is falling into disuse.