快速答案
passar 把时间视为经历；gastar 把钱、时间或精力视为被消耗的资源。
可靠的方法是先判断这个词在句子里的功能，再翻译。
每个词的作用
passar
to spend or pass time
Use passar for experiencing a period or using time in an activity.
gastar
to spend or use up
Use gastar for consuming money, time, energy, or another limited resource.
如何选择
- passar: Choose passar if the sentence points to experiencing a period or using time in an activity.
- gastar: Choose gastar if the sentence points to consuming money, time, energy, or another limited resource.
例句
Passei duas horas lendo.
I spent two hours reading.
Gastei cem reais no mercado.
I spent one hundred reais at the market.
常见误区
With time, both may work but the viewpoint changes: passar duas horas lendo is neutral; gastar duas horas can stress the cost.
放到语境中练习
从你的真实生活中选一个句子，写两遍：一次用 passar，一次用 gastar。如果两个版本都可以，说明意思怎样变化。