Number of sets?

Hello Everyone,

just a quick question for you; In all the articles I read, it seems that everytime the best range of set they advice to improve strengh and tone the body is between 3 and 4 (and 12 reps). I just wonder why in almost all the FB workouts (not all, there are some with 3 sets I believe) it's always 2 sets ? Is it still that effective ?

Thank you :)