<image>The passage below describes an experiment. Read the passage and then follow the instructions below.

Linda applied a thin layer of wax to the underside of her snowboard and rode the board straight down a hill. Then, she removed the wax and rode the snowboard straight down the hill again. She repeated the rides four more times, alternating whether she rode with a thin layer of wax on the board or not. Her friend Bob timed each ride. Linda and Bob calculated the average time it took to slide straight down the hill on the snowboard with wax compared to the average time on the snowboard without wax.
Figure: snowboarding down a hill. Identify the question that Linda and Bob's experiment can best answer.