Learn Russian: Продавец дал мне три розовые гвоздики и четыре жёлтые розы. - The seller gave me three pink carnations and four yellow roses.

When using the numbers 2, 3, and 4 in the Nominative or inanimate Accusative cases, the following noun goes into the Genitive singular. However, the rule for adjectives depends on the noun's gender. For feminine nouns like гвоздика and роза, the adjective takes the Nominative/Accusative plural form (розовые, жёлтые). If the nouns were masculine or neuter, the adjectives would typically be in the Genitive plural.

What case are the nouns гвоздики and розы in?

They are in the Genitive singular. After the numbers 2, 3, and 4 (when the phrase is the subject or an inanimate direct object), the noun itself must be Genitive singular. Because these are feminine nouns ending in -а, their Genitive singular forms happen to look exactly like their Nominative plural forms, but grammatically they are functioning as singular here.

Why do the numbers три and четыре look like they are in the Nominative case if they are the direct object of the verb дал?

They are actually in the Accusative case because they are the direct object of дал (gave). However, because flowers are inanimate objects, the Accusative forms of the numbers три and четыре are identical to their Nominative forms. If you were talking about animate nouns (like animals or people), you would use the animate Accusative forms, which look like the Genitive.

Is the word related to the Russian word for nails?