Evaluate the telescoping product by writing each factor as a ratio: (1 + 1/2) * (1 + 1/3) * (1 + 1/4) * ... * (1 + 1/150) = ?

Difficulty: Medium

Correct Answer: 75.5

Explanation:


Introduction / Context:
This question tests the technique of telescoping products in number theory and arithmetic simplification. By expressing each factor (1 + 1/n) as a simple fraction, most intermediate terms cancel, leaving only the first denominator and the last numerator. Recognizing this pattern saves time and avoids cumbersome multiplication.



Given Data / Assumptions:

  • Product is (1 + 1/2)(1 + 1/3)(1 + 1/4)...(1 + 1/150).
  • All factors are positive rational numbers.
  • We can rearrange factors and simplify exactly (no rounding).


Concept / Approach:
Write 1 + 1/n as (n + 1)/n. Then the entire product becomes a chain of fractions whose adjacent terms cancel (telescope). Only the first denominator and the last numerator remain after cancellation.



Step-by-Step Solution:

For each n from 2 to 150: 1 + 1/n = (n + 1)/n.Product = (3/2) * (4/3) * (5/4) * ... * (151/150).All interior numerators/denominators cancel, leaving 151/2.151/2 = 75.5.


Verification / Alternative check:
Compute a smaller sample, e.g., (1 + 1/2)(1 + 1/3)(1 + 1/4) = (3/2)(4/3)(5/4) = 5/2; the same cancellation pattern holds, confirming the approach.



Why Other Options Are Wrong:
50.5, 65.5, 105, and 151 arise from partial telescoping or forgetting to divide by 2 at the end. Only 75.5 equals 151/2.



Common Pitfalls:
Not converting to (n + 1)/n, multiplying straight across, or truncating the sequence boundaries incorrectly (starting at n = 1 would break the pattern).



Final Answer:
75.5

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