Answer: Choice D
None of these statements must be true
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Step-by-step explanation:
Let's go through the answer choices one at a time.
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A)
Consider the set {4,5,6}. It has a mean of (4+5+6)/3 = 15/3 = 5. We add up the values and then divide by the number of values (3 in this case).
Now consider the set {3,5,7}. I've added 1 to the largest element and subtracted 1 from the smallest. This will spread the data set out further. The mean is still 5 because (3+5+7)/3 = 15/3 = 5. The center hasn't changed. But the data is more spread out so the variance is larger for this new set.
Therefore, the sets {4,5,6} and {3,5,7} do NOT have the same variance. We cross choice A off the list.
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B)
Recall that
For example, if the variance is 36 then the standard deviation would be
Because of the connection of the standard deviation and variance, both measure how spread out a set is. Furthermore, it means the sets {4,5,6} and {3,5,7} do NOT have the same standard deviation. We can cross choice B off the list.
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C)
This statement is clearly not true because the sets {4,5,6} and {3,5,7} are not the same, but they produce the same mean. We can cross choice C off the list.
Choice D is the only thing left so it must be the final answer.