The general principle is:
faced with the choice of having one big pizza whose diameter is α times the diameter of the small ones, or β small ones- choose the big one if α>sqrt(β).
In the private case above α=1.5>sqrt(β)≈1.41 => choose one big pizza. pic.twitter.com/DIAxVUoTui

— Rational Walker (@rationalwalker) January 7, 2019