Yikes! Good lord they're definately trying to get their money's worth out of you. When i've taken med/surg assignments i've either started with five and finished the night with the same five, or taken 3 to start and accepted 2 from ER throughout the night if we had admissions.
Something i'd suggest however if you go that route you may find yourself on someones **** list, find out what the nurse to patient ratio is supposed to be by your state, not the hospital, if they're going over that nurse to patient ratio, you literally can refuse the shift. Remember it's your license, not the hospitals. If a patient dies due to you not having enough time to get this med or that treatment done, is the hospital going to ante up to defend you and say "hey she/he was doing what we told them to do." I think not.
My best advice would be find another place to work, and take what you learned from this place to the next interview, ask questions, like what are the norms for a med/surg unit patient assignment, or how many beds does the hospital have in relation to how many IV pumps? simple questions like that will show your sharp for one, but also not a sucker either. A normal hospital should be able to accomodate at least 3/4 if not more of every hospital bed with at least one IV pump. I've seen ICU patients monopolize up to 3 pumps at once, and at 10 beds in ICU, and most of them aren't there cuz they want to be, and desperately need what they monopolize, keep that in mind as well. But i'd say, for sure start looking for another place to work, it's definately not a safe environment to work in.