(3×197-2×1)×0.4×1
————————————×1.5=
3×197
0.5979695431 and rounded 0.6%
So according to my calculations there is a 0.6% chance of catching a wild Zapdos with a premier ball
Note:
This is for a Zapdos that would have a totally max HP stat at lv.50. If you give the HP of your Zapdos at lv.50, I can give you the precise percentage of the chances you had :)
Ok, now that I have your Zapdos' HP, the calculations are as followed:
(3×158-2×1)×0.4×1
———————————×1.5=
3×158
0.5974683..., rounded 0.6
As you can see the chance remains 0.6% :)