Four people enter an elevator (going up) on the first floor. Assume

that each person presses the button for one of floors 3 through 10 at random, inde- pendently of all others. Find the chance that they press four different buttons. Start

by filling in the blanks in the following sentence; the first two blanks should be filled with integers. "This experiment is like throwing (blank) balls independently at random into (blank) boxes labeled (blank)." Then imagine where the balls must land to make the event occur.