Cause i have been on losing streaks on team ranked as my team wasn't serious in playing them. So just wonder if it affects my own hidden MMR since the losses is accounted for in my ranked w/l.
Your MMR is different in every queue. Your MMR for normal games is separate from your Dominion games, which is separate from ranked 5s, etc. This means that winning or losing in one queue will not affect your standing in other queues. For your specific example, losing a lot on a ranked 5s team will not influence your solo queue mmr. Further, if you join another team, your mmr with that team will be independent of your mmr with the first.
I'll take a stab at listing all of the different queues:
- Normal 5s
- Ranked 5s (different MMR for each team!)
- Ranked Solo
- Normal 3s
- Ranked 3s (Again, different MMR for each team)
(Edit) There is a very recent red post indicating that this might change (emphasis mine):
We're aware why this happens in Normal Modes, and have a fix planned for it in a future matchmaking upgrade. This basically happens when Ranked players play a lot of ranked and get into the upper tiers, but don't play Normal as much--their Normal ratings lag behind their true skill level.
Yegg and Socrates have fixes in the works so in the future a player's rating will be adjusted slightly based on their underlying skill across all the game modes. We want to be careful not to overkill with the fix as well because we do realize some Ranked players use Normal Modes to play with their friends or practice new strategies/champions too.
My original answer is correct right now, but Lyte's post indicates that it will change in the future. When the change will happen and the specifics of the "slight" effect are currently unknown.