Some time ago I took a Russian test that contained the following question:
В об(о,е)их коробках оказались семена.
1) обоих
2) обеих
3) оба варианта корректны
4) оба варианта некорректны
I chose answer 2 and got zero points for that question, whilst a coursemate of mine chose option 3 and got her answer marked as right.
I'm very much confused. As far as I understand and verified on the Internet, feminine nouns in the prepositional case require обеих, which means that choosing обоих for a feminine noun in the prepositional case is a mistake.
I asked the coursemate as to why she had chosen answer 3, and she said she believed that in conjunction with a feminine noun in the prepositional case, it is okay to use either form - обоих and обеих.
I did some research in Google and found that обоих is indeed often used in conjunction with feminine nouns in the prepositional case, and here are some examples:
В одной коробке в 6 раз больше ручек, чем в другой. А в обоих коробках 84 ручки. Сколько ручек в каждой коробке? (Source)
Заказывала два размера 35.5 и 36.5, на обоих коробках указан 37. Сами кроссовочки хорошенькие. (Source)
Копирайт на обоих коробках гласит 2004 год. В коробке с SV96 лежат отлитый в синий пластик кузов, 3 синих, 4 черных, 2 хромированных и 2 прозрачных литники. (Source)
But such usage, albeit common, seems to be formally against the grammatical rules as they are written.
So what is the correct answer to the test question? Do I have a strong case to challenge the score given to me by the teacher?