Testing a Paper Towel Claim
A company advertises that its paper towel "absorbs 40% more water than the leading brand." A student wants to test this. She has two rolls of towels: Brand X (the advertised one) and Brand Y (the leading brand). She plans one trial: she will pour 20 mL of water onto one sheet of each towel and compare how much water each sheet holds. Her teacher points out that one trial per brand is not enough to support a conclusion, and that other variables could affect the result. The student has limited time and materials: she can do 5 trials per brand, and she has a graduated cylinder, a balance, and a timer.
1. Identify one controlled variable the student should keep the same and explain why it matters.
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A good controlled variable is the size (area) of each towel sheet. If one sheet is larger than the other, it could absorb more water simply because it has more material, not because the brand is more absorbent. Other acceptable controlled variables include the amount of water poured (20 mL), the water temperature, the time the towel is allowed to soak, and how the towel is handled. Keeping these the same ensures that any difference in water absorbed can be attributed to the brand, which is the variable being tested.
2. Describe how the student should use her 5 trials and measurements to make a fair comparison, and what she should do with the results.
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She should run 5 trials for Brand X and 5 trials for Brand Y, using the same sheet size, the same 20 mL of water, and the same soaking time for every trial. For each trial she should measure the mass of water absorbed (for example, by weighing the towel before and after) or measure the volume of water left in the graduated cylinder. Then she should compare the averages of the 5 trials for each brand rather than relying on a single result. Averaging reduces the effect of random variation. She should also note the range or spread of the results to judge whether the difference is consistent. Only then can she judge whether the 40% claim is supported.