Difficulty: Easy
Correct Answer: 511
Explanation:
Introduction / Context:
The series matches the form n^3 − 1 for consecutive integers n. Recognizing this lets you continue by moving to the next integer and applying the same formula.
Given Data / Assumptions:
Concept / Approach:
Next n = 8 ⇒ next term = 8^3 − 1 = 512 − 1 = 511.
Step-by-Step Solution:
Identify formula: term(n) = n^3 − 1.Compute for n = 8: 8^3 = 512.Subtract 1 ⇒ 511.
Verification / Alternative check:
Differences between terms grow roughly as 3n^2 − 3, consistent with cubic behavior. The explicit computations confirm the pattern exactly.
Why Other Options Are Wrong:
481, 391, 421, and 450 are not equal to 8^3 − 1 and do not continue the exact n^3 − 1 rule.
Common Pitfalls:
Misreading 124 as 125 (a perfect cube) and assuming cubes themselves, not “cubes minus one.” Always check each term.
Final Answer:
511
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