Ranked LP

Hey I was wondering if someone could explain the scale for how you lose or gain LP. I am asking because it seems I have really good games, 17/9/12 for example, and I lose 20+ LP because my team around me is bad. Is there a scale that allots so many points? Like this person went 22/2/15 and lost they gained 5 points but they lost the game as a whole so minus 25 points or is it just random?