## Item CR015006: To determine the effect of speed on a truck's gas mileage, is important that trucks of the same weight be compared because if the trucks didn't have the same weight, it wouldn't be possible to learn about the effect of speed on gas mileage.

A consumer group is interested in the effects of the speed and the weight of a truck on a truck’s gas mileage. A truck’s gas mileage is the number of miles it can travel for each gallon of gas it uses.

First the group decides to test if a truck’s speed affects its gas mileage. They take two identical trucks and drive one at 30 miles/hour and the other one at 45 miles/hour on the same road. They make sure that the two trucks have the same weight.

Why is it important that the two trucks have the same weight?

- By using trucks of the same weight, the group can learn about both the effect of the weight and the effect of the speed on the gas mileage.
- By using trucks of the same weight, the group can learn about the effect of the weight on the gas mileage.
- If the trucks do not have the same weight, the group cannot learn about the effect of the speed on the gas mileage.
- It is NOT important for both trucks to have the same weight because the group is not testing the effect of the weight on the gas mileage.

- Distribution of Responses

- Students Responding Correctly

Group | Correct | Total | Percent |
---|---|---|---|

Overall | 1172 | 2502 | 47% |

Grades | |||

6–8 | 588 | 1421 | 41% |

9–12 | 578 | 1072 | 54% |

Gender | |||

Male | 601 | 1228 | 49% |

Female | 551 | 1235 | 45% |

Primary Language | |||

English | 1020 | 2145 | 48% |

Other | 115 | 292 | 39% |