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Each of 2010 boxes in a line contains on...

Each of 2010 boxes in a line contains one red marble and for `1lekle2010`, the box is the `k^(th)` position also contain `k` white marbles. A child begins at the fist box and successively drawn a single marble at random each box in order. The stops when be fist draws a red marble. Let `p(n)` be the probability that the stops after drawing exactly `n` marbles. The possible value (s) of `n` for which `p(n)lt 1/ 2010` is:

A

44

B

45

C

46

D

47

Text Solution

AI Generated Solution

The correct Answer is:
To solve the problem, we need to find the probability \( p(n) \) that the child stops after drawing exactly \( n \) marbles, and determine the possible values of \( n \) for which \( p(n) < \frac{1}{2010} \). ### Step-by-Step Solution: 1. **Understanding the Problem**: Each of the 2010 boxes contains one red marble and \( k \) white marbles in the \( k^{th} \) box. The child draws marbles from the boxes in order until they draw a red marble. 2. **Calculating Probabilities**: - The probability of drawing a white marble from box \( k \) is: \[ P(\text{White from box } k) = \frac{k}{k + 1} \] - The probability of drawing a red marble from box \( k \) is: \[ P(\text{Red from box } k) = \frac{1}{k + 1} \] 3. **Condition for Stopping**: The child stops after drawing \( n \) marbles if they draw white marbles from boxes 1 to \( n-1 \) and a red marble from box \( n \). Therefore, the probability \( p(n) \) can be expressed as: \[ p(n) = \left( \prod_{k=1}^{n-1} \frac{k}{k+1} \right) \cdot \frac{1}{n+1} \] 4. **Simplifying the Product**: The product \( \prod_{k=1}^{n-1} \frac{k}{k+1} \) simplifies to: \[ \prod_{k=1}^{n-1} \frac{k}{k+1} = \frac{1}{n} \] Therefore, we have: \[ p(n) = \frac{1}{n} \cdot \frac{1}{n+1} = \frac{1}{n(n+1)} \] 5. **Setting Up the Inequality**: We need to find \( n \) such that: \[ \frac{1}{n(n+1)} < \frac{1}{2010} \] This leads to: \[ n(n+1) > 2010 \] 6. **Finding Values of \( n \)**: We need to find integer values of \( n \) that satisfy this inequality. We can test values of \( n \): - For \( n = 44 \): \[ 44 \times 45 = 1980 \quad (\text{not greater than } 2010) \] - For \( n = 45 \): \[ 45 \times 46 = 2070 \quad (\text{greater than } 2010) \] - For \( n = 46 \): \[ 46 \times 47 = 2162 \quad (\text{greater than } 2010) \] - For \( n = 47 \): \[ 47 \times 48 = 2256 \quad (\text{greater than } 2010) \] 7. **Conclusion**: The possible values of \( n \) for which \( p(n) < \frac{1}{2010} \) are \( n = 45, 46, 47, \ldots \). ### Final Answer: The possible values of \( n \) for which \( p(n) < \frac{1}{2010} \) are \( n \geq 45 \).
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