In the Cub Scouts, the Pinewood Derby is a big event. Little boys, with a bit of help from their daddys, carve a 6-inch race car and attach wheels. Several cars race down an incline and a winner is declared. Sometimes the winner even gets his picture in the paper. Daddys often know of ways to increase the speed of the car. Smoothing the axle with emery cloth (a kind of sandpaper for metal) will reduce the race time one second. Putting graphite (a lubricant) on the axle will reduce the race time three seconds. Suppose some ingenious daddy did both to his son's car. Which change in that car's race time is not indicative of an interaction between emery cloth and graphite?
A) decrease 4 seconds
B) decrease 0 seconds
C) decrease 10 seconds
D) increase 2 seconds.

Question

Quizplus · Accepted Answer

Using emery cloth reduces the time by 1 second, and using graphite reduces it by 3 seconds. Without interaction, the total reduction should be 1 + 3 = 4 seconds. Choices B, C, and D suggest interactions because they deviate from the expected 4-second reduction.

In the Cub Scouts, the Pinewood Derby Is a Big