Ejemplos fáciles con los sustantivos problema, mapa, sofá y día

Why is “problema” masculine in Spanish if it ends in -a?

Beginners learn that nouns ending in -a are usually feminine, so they expect “la problema”. That is wrong. It is el problema. A small group of common words end in -a but are masculine, many of them from Greek: el problema, el mapa (the map), el sofá (the sofa), el día (the day), el tema (the topic), el clima (the climate). You just learn these as exceptions.

The clip lists four of them with example sentences: el problema de matemáticas estuvo muy difícil (the math problem was very hard) and el día de hoy es muy hermoso (today is very beautiful). Words ending in -ma like problema and tema are the most common offenders.