The conclusion is valid because they tested two different brands. The conclusion is invalid because the test had multiple variables. The conclusion is valid because they conducted the investigation in a lab. The conclusion is invalid because the real names of the batteries were hidden.
I gave my students this multiple choice question: In a lab investigation, students use Brand X batteries in a flashlight and Brand Y batteries in a radio. After two hours, the flashlight stops working, but the radio continues to work. As a result, the students conclude that Brand Y batteries last longer. Which statement about the conclusion of the investigation is most accurate?

Only one answer is correct among these 4 choices:
- The conclusion is valid because they tested two different brands.
- The conclusion is invalid because the test had multiple variables.
- The conclusion is valid because they conducted the investigation in a lab.
- The conclusion is invalid because the real names of the batteries were hidden.

Could you tell me which one is correct?

The conclusion is invalid because the test had multiple variables.