LP Issue?

Before the last ranked game I played, it showed that I had 80 LP. I just now won another ranked game, and I was told that I gained 20 LP. However, when I check, it shows that I only have 90 LP total. I'm still kind of newer to the whole ranked and LP system, but I do know that 80 + 20 does not = 90. I was told by a friend that once you get to 100 LP, you have a chance at promotion. Was he wrong, or is something occurring that only gave me 10 LP instead or 20?

The image shows the amount of LP I had after my game with Vi.