Cards numbered 1 to 200: A card is drawn uniformly at random. What is the probability the number on it is a perfect cube?

Difficulty: Easy

Correct Answer: 1/40

Explanation:

Introduction / Context:We need the density of perfect cubes among the integers 1 through 200. Recognize that cubes grow quickly, so only a few lie within this range.

Given Data / Assumptions:Numbers are 1,2,3,…,200 with equal probability; perfect cubes are n^3 for integer n ≥ 1.

Concept / Approach:Find the largest n with n^3 ≤ 200. Then probability = (count of cubes)/200.

Step-by-Step Solution:

1^3 = 1, 2^3 = 8, 3^3 = 27, 4^3 = 64, 5^3 = 125, 6^3 = 216 > 200Cubes ≤ 200 are 1, 8, 27, 64, 125 ⇒ 5 numbersProbability = 5/200 = 1/40

Verification / Alternative check:Use floor of cube root: ⌊∛200⌋ = 5 ⇒ count = 5; divide by 200.

Why Other Options Are Wrong:3/40 and 7/40 miscount; 19/40 is not plausible given rarity of cubes.

Common Pitfalls:Including 216 (6^3) erroneously or forgetting 1 is a cube.

Final Answer:1/40

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