Learn Russian: Открытие выставки было пятого марта тысяча девятьсот девяносто восьмого года. - The opening of the exhibition was on the fifth of March nineteen ninety-eight.

When saying on a specific date in Russian, the entire date phrase takes the Genitive case. The day (пятого) is a neuter ordinal number because the neuter word число (date) is implied. The month (марта) is also in the Genitive to mean "of March."

Why are the words тысяча девятьсот девяносто in their normal dictionary form, while восьмого is in the Genitive?

In Russian, years are compound ordinal numbers (literally "the 1998th year"). The golden rule for these is that only the very last word is an ordinal number that changes its case! Therefore, тысяча девятьсот девяносто stays in the basic Nominative case, and only восьмого changes to the Genitive, along with the word года (of the year).

Why is the verb было in the neuter form when the exhibition (выставка) is feminine?

The main subject of the sentence is открытие (the opening), which is a neuter noun ending in -е. The word выставки is in the Genitive case ("of the exhibition") and is not the subject. Since the past-tense verb always agrees with the subject, было takes the neuter ending to match открытие.

Why does выставка change to выставки in this sentence?