Two additives to Portland cement are being tested for their effect on the strength of concrete. 21 batches were made with Additive A, and their strengths showed standard deviation s, = 41.3. 16 batches were made with the same percentage of Additive B, and their strengths showed standard deviation s, = 26.2. Assume that the strengths of concrete follow a normal distribution. Is there evidence at the 1% level of signifi- cance that the concrete made with Additive A is more variable than concrete made with Additive B?

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