This is the 2894th most frequent Spanish word.
simples
Plain or simple.
Here, 'simples' modifies 'cosas', indicating 'things that are simple or uncomplicated'.
Me gustan las cosas simples de la vida.
I like the simple things in life.
In this sentence, 'simples' describes 'problems', emphasizing their easiness or lack of complexity.
Los problemas eran simples, pero los ignoraron.
The problems were simple, but they were ignored.
'Simples' indicates that the exercises are straightforward or easy to understand.