It's funny that you asked.

Actually, I was bored and did some Normal Gacha science a while ago. I was writing down results of my pulls to get percentage chances, since the're not listed anywhere AFAIK.
Recorded
4220 pulls on Nutaku. Here are the rates.
2* - 3903 -
92.49%
3* - 232 -
5.50%
4* - 11 -
0.26%
Manyu - 73 -
1.73%
Ampy - 1 -
0.02%
I've also written down some pulls on DMM, and rates seem to be pretty much the same.