Table salt is being fed to a vibrating screen at the rate of 3000 kg/hr.The desired product is the 48/65 mesh fraction.A -48 + 65-mesh screen are therefore used, the feed being introduced on the 48 mesh screen, the product being discharged from the 65-mesh screen. During the operation it was observed that the average proportion of the oversize: product: undersize was 2:1 ½:1. Calculate the effectiveness of the screens? What conclusions can you draw from the values computed versus the given proportion?