How to set drop? (%)

Hi all,
I'm searching to make the drop, but I don't know what % use.
For example I have tried this drop:

Code:

Group    Villo1_101{
 type	limit
 level_limit 10
 Mob 171
 1 27992  1    0.1
 2 27993  1    1
 3 27994  1    2
}

But I drop only 27994 item difficulty with 200% drop rate.
I had thought about doing it this way:
12:01 hard to drop
0.1 average drop
1 drop easy

Can anyone help me to choose the percentage of drop please?

Regards.