Learn Russian: Значит, огранка алмаза понравилась только двоим покупателям. - So, only two buyers liked the cut of the diamond.

Двоим is the dative case of the collective numeral двое (a group of two). Collective numerals are often used with masculine animate nouns like покупатель (buyer). Using the regular cardinal numeral двум would also be grammatically correct here, but the collective form is a stylistic choice that emphasizes the buyers as a specific, enclosed group.

How do we form the oblique cases for collective numerals like двое?

Collective numerals decline very similarly to plural adjectives. The nominative is двое, but in the dative case required by the verb понравиться, it takes the plural adjective ending -им, becoming двоим. This matches the dative plural noun покупателям.

Why is the verb понравилась in the feminine singular form instead of plural?

With the verb понравиться (to appeal to / to be liked), the thing being liked is the grammatical subject. Here, the subject is огранка (the cut), which is a feminine singular noun. The verb takes the feminine past tense ending -а to match it. The buyers are in the dative case (двоим покупателям) because they are the indirect objects experiencing the liking.

Why is there a comma after Значит?

In this sentence, значит is used as an introductory word meaning 'so' or 'therefore' to express a conclusion. Introductory words in Russian are separated from the rest of the sentence by commas. If it were functioning as the verb meaning 'it means', there would be no comma.