Здравствуйте,
I am novice to this forum and to the Russian language. Can you please explain how come the word проезда switches from про to the по- in поездку?
Для проезда в метро надо купить карточку то есть билет. Карточка на одну поездку стоит пятнадцать рублей.
Большое спасибо
It doesn't. Проезд and поездка are two different nouns.
Проезд is masculine, somewhat "officialese", and refers to "riding" as a concept. It's also uncountable (in this meaning; not in its other one where it means "thoroughfare".)
Поездка is feminine, stylistically neutral, and means "ride" or "trip". As such, it's countable.
