stuff rep ranges - think in terms of weights.
You can do 3 reps with a moderate weight or you could do 10, that's why I prefer to use percentage of 1RM.
Lift between 70-85% for Mass. >85% for strength and between 40-60 for power.
As far as reps go, use your imagination. You could with 70% of 1RM do 4x9, or 6x6 - it doesn't matter much. Total Load under tension is what counts, both rep scheme still give you the same 36 total reps and tonnage. You should vary the schemes though periodicly. All that matters is that Tonnage goes up over time.
I agree with the 1RM therory.I just finished a book "Serious Strength Training" which is put out by Human Knetics.I hightly recomends it.
"The longer the muscles remain in tension,the more strongly activated the muscle's metabolism becomes.Which stimulates muscle growth to new highs"