Stat bonus modifiers are additive.
If you have 1b dex with zero modifiers, you have 1b dex.
50% modifier gives you 1.5b dex.
If you use tyro, it adds 500% to your modifier, giving you 550% total modifier which gives you 6.5b dex.
Armor that gives you a stat modifier like sentinel or vanguard just add to your modifier.
For example if you have 50% modifier to start.
Vanguard armor gives you +150% modifier.
Tyro gives you +500% modifier.
Total modifier is 700%
At 1b dex you end up with 8b dex with a 700% modifier.
Smoke and tear gas are different. Someone else can dig into the details of those...
Also, not sure what the guy above this post is talking about with armor... Armor has nothing to do with hit chance or defensive effectiveness. Armor reduces the damage you take by a percentage, after damage from stats is calculated. For example if someone hits you in a spot where you have no armor and they deal 1000 damage, you take 1000 damage. But if that hit were to hit an armor spot and you have 25 armor, you take 25% less damage. So you'd only end up taking 750 damage instead of 1000.