A common mistake among Spanish speaking learners of English is to say "subject + are" instead of "there +are" when talking about the existence of a number of things. To clarify who you are referring to, use of + object, e.g. of us, of them, of you.
Somos veinte personas - There are twenty of us (We are twenty people)
¿Cuántos sois? - How many of you are there? ( How many are you?)
Son muchos los problemas que causa la comida rapida - Fast food causes many problems/ There are many problems caused by fast food