Let be the amount of salt (in kg) after minutes. Then . The amount of liquid in the tank is 100 L at all times, so the concentration at time (in minutes) is and
A. You run 4 miles: 4 Rob ran half as far as you: 0.5 * 4 Tim ran half as far as Rob: 0.5 * (0.5 * 4) Nicole ran half as far as Tim: 0.5 * (0.5 * (0.5 * 4)))