Questions & Answers about Я добавил к платежу около пятидесяти рублей.
Why do we use the preposition к before платежу?
The verb добавить (to add) pairs with the preposition к plus the Dative case to show what you are adding something to. Since платёж (payment) is a masculine noun ending in a consonant, it takes the -у ending to become к платежу.
Why is the number 50 written as пятидесяти?
The preposition около (around/about) forces the following word into the Genitive case. When declining compound numbers like 50 (пятьдесят), both halves of the word change. The Genitive of пять is пяти, and the Genitive of десять is десяти, combining to make пятидесяти.
Why is it рублей and not рубля?
Numbers from 5 onward generally require the noun that follows them to be in the Genitive plural. The Genitive plural of рубль is рублей. Even though the number itself is in the Genitive case because of около, the noun's form remains рублей.
Why use the perfective verb добавил here instead of the imperfective добавлял?
The perfective aspect is used here because it describes a single, completed action in the past. The speaker added the money one time, and the action is finished. If they were adding it repeatedly or describing the ongoing process, they would use добавлял.