Sometimes one is mystified at the startling reductions some people make in their prices and wonders on what principle the reductions are based. To quote an example three years ago a friend offered me a used typewriter for $1024. A year later he offered me the same for $640 and last year he wanted $400 and now he is willing to sell it to me for $250. But I have decided to buy it when he reduces next time. If he does a consistent reduction, at what price will he offer the typewriter to me next?