This looks to be a straight forward puzzle, but I expect the 140 characters limit has lead to the puzzle being set without enough rigour, or was it just another example of a pizza chain and it’s careless approach to maths? As I see it, there are at least 2 different interpretations to the question provided.
1) Those 2 people order 2 pizzas in 2 minutes, therefore their rate of ordering is 1 pizza/minute. So if they continue to order more pizzas at that rate them alone will order all 500 in 500 minutes (i.e. the answer is 2 people).
2) If the restaurant is full of people and everyone orders just one pizza (not mentioned in the question so would have to be a heavy assumption) and everyone we consider orders at the same rate as the original couple then it will take 500 people (if they’re ordering in series).
3) Anyone have any other interpretation?
As it stands I believe that #1 is the most accurate answer, regardless of how greedy it makes those 2 look. It comes down to the question referring to the rate at which the couple is ordering their pizzas at: they are ordering at a rate of 1 pizza per minute so just the 2 of them will order the full quota in the desired time.
Pizza Express have chosen the second option, which I feel only works as an answer if the question is rephrased. They can blame 140 characters, but I blame bad maths… #mathspolice I turn the investigation over to you.