Only two explanation can account for the wage discrepancy between two factories both of whom employ equal number of workers. 1) different working hour 2) different hour wage rate. In this piece of information, since the wages in two factories are compared upon annul working time, one hidden premise is that the regular working hour each day throughout the whole year, thus the overall regular time in a year, be the same in both factories. Then coupled with this unstated premise, D excludes different working time as a possible valid explanation for the discrepancy, leaving a higher hour rate as the only choice. |