What are the % chance of a random encounter each time you enter a patch of grass ? (Section of ocean)?

Question

Just curious, it seems to be so high in B/W2 T_T

Answer 1

The rate of Pokémon encounter is determined from a simple mathematical formula:
1 in (187.5 / ( x )) per step
Let x equal the a value which determines how rare the Pokémon is. The higher the encounter rate, the more common the Pokémon is.
Encounter-rate table
Encounter type Encounter rate
Very common 10
Common 8.5
Semi-rare 6.75
Rare 3.33
Very rare 1.25

Check here for more info. -----> http://bulbapedia.bulbagarden.net/wiki/Tall_grass