At Level 100
1 IV = 1 stat point
I'll use your Greninja example.
| 0 IVs | 95 Base Attack (+0 points)
| 1 IV | 96 Base Attack (+1 point)
| 31 IVs | 126 Base Attack (+31 points)
At Level 50
IVs affect stats a bit differently at Level 50. Every other IV boosts the stat by one point. For example, 30 IVs in Attack are the same as 31 IVs in Attack. However, as soon as any EVs are put into that 30 IV stat, you ultimately lose a stat point.
| 30 IVs | 252 EVs | 146 Attack
| 31 IVs | 252 Evs | 147 Attack