Julio bought 3/5 lb of potato salad or 0.6 lb of potato salad. Wilma bought 5/4 of the amount Julio did or 1.25 of what he did. So Wilma bought 1 equal amount Julio did - so 0.6 plus 0.25 of 0.6 which is 0.15. So Wilma bought 0.6 + 0.15 or 0.75 of a pound of potato salad.
