На кассе самообслуживания я случайно пробила купон два раза и попросила кассира помочь.

At the self-checkout I accidentally scanned the coupon twice and asked the cashier to help.

Breakdown of На кассе самообслуживания я случайно пробила купон два раза и попросила кассира помочь.

• я: I
• на: at
• и: and
• помочь: to help
• два: two
• случайно: accidentally
• попросить: to ask
• купон: coupon
• касса самообслуживания: self-checkout
• пробить: to scan (ring up)
• раз: time
• кассир: cashier

Questions & Answers about На кассе самообслуживания я случайно пробила купон два раза и попросила кассира помочь.

Why does it say на кассе самообслуживания and not в кассе?

На is used with places understood as a point/spot where an action happens (a station, a desk, a counter, a checkout): на кассе, на почте, на стойке регистрации.
В would sound like inside a physical container, which a checkout isn’t.

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What case is кассе in на кассе, and why is it spelled кассе?

It’s prepositional case (singular) after на meaning location.
касса → (на) кассе is a standard spelling change for many feminine nouns ending in -а: школа → в школе, касса → на кассе.

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Why is it кассе самообслуживания? What case is самообслуживания?

самообслуживания is genitive singular. It means “of self-service,” so the phrase literally is checkout (of) self-service = “self-checkout.”
This is very common in Russian: отдел игрушек (toy department), зал ожидания (waiting hall), касса самообслуживания.

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Does касса самообслуживания mean the machine or the area?

Usually it refers to the self-checkout station/register (the place/machine where you scan items). Context decides, but in stores it’s understood as the self-checkout register you’re using.

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Why is the verb пробила used? I thought пробить means “to punch through.”

In retail Russian, пробить commonly means to scan / ring up / process at the register.
So пробила купон = “I scanned/entered the coupon.”

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Why is it пробила (feminine)? What if the speaker is male?

Past tense in Russian agrees with the subject’s gender/number.

• Female speaker: я пробила, я попросила
• Male speaker: я пробил, я попросил
• Plural: мы пробили, мы попросили

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What does случайно modify, and can it move in the sentence?

случайно (“accidentally”) modifies пробила (the scanning action).
It’s flexible:

• Я случайно пробила купон два раза. (neutral)
• Случайно я пробила купон два раза. (more emphasis on “accidentally”)
• Я пробила купон два раза случайно. (also possible)

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Why is два раза used, and can I say дважды instead?

два раза = “two times,” very common in everyday speech.
дважды also means “twice” and is a bit more concise/formal. Both work:

• пробила два раза
• пробила дважды

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What case is купон in пробила купон, and why?

It’s accusative because it’s the direct object of пробить (to scan/ring up something).
For inanimate masculine nouns like купон, nominative and accusative look the same: купон.

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Why is it попросила кассира, not попросила кассир or попросила кассиру?

попросить кого? takes the person asked in accusative.
Because кассир is animate masculine, its accusative singular looks like the genitive:
кассир → кассира (this is a key rule for masculine animate nouns).

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Why is the structure попросила кассира помочь (person + infinitive)? Could it be попросила помочь кассира?

The natural pattern is попросить кого (сделать что):
попросила кассира помочь = “asked the cashier to help.”
попросила помочь кассира sounds wrong because it misplaces кассира; it should be the object of попросила, not of помочь.

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Why are both verbs perfective past (пробила, попросила)?

Perfective is used for completed, one-time actions in the past:

• пробила = the (accidental) scanning happened and is done
• попросила = the request was made (completed act of asking)
  If you wanted to emphasize an ongoing/repeated process, you might use imperfective (depending on context), but here the events are discrete and finished.