Difficulty: Medium
Correct Answer: 100
Explanation:
Introduction / Context:This is a classic number puzzle modeled as an algebraic equation. It uses staged consumption (half of the arrows, then fixed amounts, then an amount depending on the square root of the original total) to form a solvable equation in the original number of arrows, n.
Given Data / Assumptions:
Concept / Approach:Translate the staged usage into the equation: (n/2) + 6 + 3 + (4*sqrt(n) + 1) = n. Solve by isolating sqrt(n), converting to a quadratic in t = sqrt(n), and choosing the positive root only (since counts are nonnegative).
Step-by-Step Solution:
Total used = n/2 + 6 + 3 + (4*sqrt(n) + 1) = n/2 + 10 + 4*sqrt(n).Set equal to n: n/2 + 10 + 4*sqrt(n) = n.Rearrange: 10 + 4*sqrt(n) = n/2 ⇒ multiply by 2: 20 + 8*sqrt(n) = n.Let t = sqrt(n). Then n = t^2, so t^2 − 8t − 20 = 0.Solve: t = [8 ± sqrt(64 + 80)]/2 = [8 ± 12]/2 ⇒ t = 10 (reject −2).Hence n = t^2 = 100.Verification / Alternative check:
Check usage: half = 50; then 6 + 3 = 9; total 59. Remaining 41. Final use = 4*10 + 1 = 41. All used.Why Other Options Are Wrong:
Common Pitfalls:
Final Answer:
100
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