The answer is Conformity. Conformity is the act of confirming or following the mainstream culture. It means that people follow the rules and standards that is being set by the current culture. During the 1950's, Americans were divided into different social group and they act according to the culture of the social groups.
By adding one more person, they each save $8 Total saving = 5 x 8 = 40 So $40 is what the 6th person has to pay. Therefore the total rent is 6 x 40 = $240.