Shouldn't that be "שתים" because the vowel is "e", not "ayi"?
In the number twelve שְׁתַּ֫יִם is shortend to שְׁתֵּים, where the Jodh is only a mater lectionis for the Tzere, not longer a consonant. Therefore you can write in the full spelling too only one Jodh.
Need that #1 place on the leaderboard
Why is it לימוד and not למידה?
Well, לְמִידָה and לִמּוּד mean mostly the same thing, being action nouns of לָמַד learn and לִמֵּד teach, after לִמּוּד shifted in meaning to studying, learning.
Thank you IngeborgHa14.