A vampire needs to suck 7 gallons of blood per week to survive.  If he sucks 2 pints of blood per person, how many people does he need to suck each day to survive?
Each day it needs to consume 7/7=<<7/7=1>>1 gallon of blood
There are 128/16=<<128/16=8>>8 pints per gallon
So he needs to suck blood from 8/2=<<8/2=4>>4 people per day
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