What is the standard deviation of set X, containing consecutive odd integers?
(1) Set consists of 10 elements
(2) The range of the set is 18
Answer: D — EACH statement ALONE is sufficient
Key Concept:
For a set of consecutive odd integers (e.g., 3, 5, 7, 9...), the common difference between terms is always fixed at 2. Standard deviation measures the spread of data, not the actual values themselves. Since the spacing between consecutive odd integers never changes, the standard deviation of such a set depends only on how many terms (n) it contains — not on which specific odd integer the set starts from.
Illustration:
Set A = {1, 3, 5} → n = 3
Set B = {101, 103, 105} → n = 3
Both sets have the exact same standard deviation because they have identical spacing—the entire set is just shifted. This confirms that SD is a function of n alone (for a fixed common difference).
Evaluating the Statements:
Statement (1): n = 10 elements
Since n is given directly, and the common difference is always 2, the standard deviation can be uniquely determined.
Sufficient
Statement (2): Range = 18 For a set of n consecutive odd integers:
2(n−1)=18 ⟹ n−1=9 ⟹ n=10
This also yields n = 10, which is enough to determine the standard deviation.
Sufficient
Both statements independently lead to n = 10, and since SD depends only on n (given the fixed common difference of 2), each statement alone is sufficient to answer the question.
Correct Answer: D