Each person will receive    of a pizza.

Their answer, 5/7, is correct if we assume the pizzas are 
all the same size. Otherwise, we'd have to go into the square
inches of pizza.  The most common size diameters for pizzas 
are 12 and 14 inches.  Their radii are half their diameters 
or 6 and 7 inches.

Suppose there were 3 14-inch pizzas and 2 12-inch pizzas.

Then the area of each 14-inch pizza would be 

, we would have 3 of those or  square
inches.

Then the area of each 12-inch pizza would be
, we would have 2 of those or  square
inches.

So the 5 pizzas would have a total of  square inches.

Then we would divide that up 7 ways and get  square inches.

Each person would get about 48.5 square inches of pizza.

Edwin