Shortcut Trick
Identify the number of terms (n): The denominators are 2, 6, 12, ..., 156, which follow the pattern n(n+1). Since 12 × 13 = 156, there are 12 terms.
Calculate Integer sum: 888 × 12 = 10656.
Calculate Fractional sum: Use the formula n/(n+1) for the series 1/(1×2) + 1/(2×3) + ... + 1/(n(n+1)).
⇒ Sum = 12/(12 + 1) = 12/13.
Combine both: 10656 + 12/13 = 10656 12/13.
∴ The correct answer is 10656 12/13.
Alternate Method
Given Expression: 888 1/2 + 888 1/6 + 888 1/12 + ... + 888 1/156
The given expression consists of mixed fractions. We can separate the integer parts and the fractional parts using the property: a b/c = a + b/c.
⇒ Total Sum = (888 + 888 + ... + 888) + (1/2 + 1/6 + 1/12 + ... + 1/156)
⇒ Since 156 = 12 × 13, the denominators are 1×2, 2×3, 3×4, ..., 12×13. This confirms there are 12 terms.
⇒ Integer sum = 888 × 12 = 10656.
⇒ Fractional part (Telescoping Series) = [1/1 − 1/2] + [1/2 − 1/3] + [1/3 − 1/4] + ... + [1/12 − 1/13].
⇒ Fraction sum = 1 − 1/13 = 12/13.
⇒ Final Answer = 10656 + 12/13 = 10656 12/13.
∴ The correct answer is 10656 12/13.
Additional Information
Mixed Fraction Decomposition
Any mixed fraction of the form A b/c can be written as A + b/c. In a series of such fractions, the whole numbers and fractions can be summed independently.
Telescoping Sum Formula
For a series of the form 1/[n × (n + k)], the general expansion is (1/k) × [1/n − 1/(n + k)]. When k = 1, it simplifies to 1/n − 1/(n + 1).
Sum of Consecutive Product Series
The sum of the first n terms of the series 1/(1×2) + 1/(2×3) + ... + 1/[n(n+1)] is always equal to n/(n+1).