Random gee-wiz information for those interested.

True percentages based on multiple pulls.

Disclaimer:
- this can apply to any gacha pulls; be it in this game or others
- this does not assume or take into account poorly-designed/rigged/weighted random engines
- randomness (math) becomes more accurate the more pulls one can make

Here is the math for pulling at least one X rarity from a multi-pull gacha.
note: the math for pulling more than one (i.e. at least 2/3/4/etc) is different and gets a bit more complicated, so we'll stick to one so people can get a feel of what the actual percentages are.

1 - ((100 - C)/100)^N
1 - ((100 - <percent chance>)/100)^<number of pulls>

example: currently a 6 star girl has a 0.5% of dropping on a single gacha pull for 5 flower gems
however, it's better to use 50 flower gems for not only 1 extra pull (10->11), but for a larger attempt as well

6 star
1 - ((100 - 0.5)/100)^11
1 - (99.5/100)^11
1 - (0.995)^11
= 0.05364542018655696690418950195313
= 5.354% for (at least) one pull out of 11 to be a 6 star

here are the remaining chances for your viewing pleasure

5 star
1 - ((100 - 6)/100)^11
1 - (0.94)^11
= 0.4937017927507942803456
= 49.37%

4 star
1 - ((100 - 30)/100)^11
1 - (0.7)^11
= 0.98022673257
= 98.02%

3 star
1 - ((100 - 63.5)/100)^11
1 - (0.365)^11
= 0.99998468131418123243611440429688
= 99.998%

as you can see, it's nearly impossible to not pull at least 1 3-star girl during an 11 pull.
it may happen 1.54 times out of 100,000 11-pulls (i.e. likely around 1.1 million girls pulled from the gacha)


final thoughts:
do know that these chances are not linear.
if you pulled 11 twice in a row, it would not double your chances for a 6-star, but because the chances are so low it very nearly would.
instead, replace the exponent with a 22 to get your answer.
the higher the chances already are, the smaller the increase will be, but regardless it will move closer to 100%

6 star (11 -> 22)
5.354% -> 10.44%
5 star (11 -> 22)
49.37% -> 74.36%



warning: the following may induce headaches, trauma, nightmare, and flashbacks.
you have been warned

sources:
https://en.wikipedia.org/wiki/Binomial_distribution
or google:
chances over multiple rolls