我在某間大型保險公司選購定期人壽保險時發現一個有趣現象：增加保額的邊際差價原來可以時上時落，最高和最低相差超過一倍。最特別是買300萬保額竟然比買250萬便宜！

如果這現象背後是有著精算的考慮，那會是因為300萬的人有著過人之處？還是受到某些政策的影響？

While I am shopping for term life insurance I have discovered that pricing can be non-monotonic. In the case illustrated below, the price of getting 3 million coverage is actually lower than that of 2.5 million. What is the actuarial logic behind this phenomenon?