"These letters are personal."
Translation:Estas cartas son personales.
Letras refers to individual letters like those in the alphabet. Cartas are letters like one would receive in the mail. Without knowing this distinction, It might be frustrating getting dinged, and the "context Nazis" on here are gonna say, "...but hoooooww cooouullldd I have known!!! REPORT IT!!..."
But, I'm with Duo on this one.
In other instances, Duolingo has accepted "letras" and "cartas" as synonymous.
As Lane pointed out "letras" are letters of the alphabet, while "cartas" are epistles such as you might mail to someone.
What is my mistake on this? " Estas letras son personales". Duo pointed "cartas" instead of "letras".
Letras are those that conform the alphabet.
Cartas is a writing that a person directs to another for give him news.
I started to writes personales instead of intimos but then moused over the word to see what duo suggested. Having had the second word trigger a fail in the past, I switched and then it marked it wrong and said personales was correct. couldn't both work?