The expression: 3/4 + 5/36 + 7/144 + ..... + 17/5184 + 19/8100 is equal to:
2023

The expression: 3/4 + 5/36 + 7/144 + ..... + 17/5184 + 19/8100 is equal to:
- A.
0.9
- B.
0.99
- C.
0.98
- D.
0.78
Show answer & explanation
Correct answer: B
Concept: For consecutive positive integers k and k+1, the fraction (2k+1)/[k2(k+1)2] simplifies exactly to 1/k2 - 1/(k+1)2 -- the difference of the reciprocals of their squares. Summing such differences for consecutive values of k telescopes: every interior term cancels, leaving only the very first and the very last term.
Application: Matching each term of the given series to this pattern:
3/4 = 1/12 - 1/22 (k = 1)
5/36 = 1/22 - 1/32 (k = 2)
7/144 = 1/32 - 1/42 (k = 3)
... the same pattern continues for k = 4, 5, 6, 7
17/5184 = 1/82 - 1/92 (k = 8)
19/8100 = 1/92 - 1/102 (k = 9)
Adding all nine differences telescopes: every middle term (1/22, 1/32, ..., 1/92) appears once with a plus sign and once with a minus sign and cancels out, leaving only 1/12 - 1/102.
1/12 - 1/102 = 1 - 1/100 = 99/100 = 0.99
Cross-check: Add just the first two terms directly: 3/4 + 5/36 = 27/36 + 5/36 = 32/36 = 8/9, which equals 1/12 - 1/32 = 1 - 1/9 = 8/9. The partial telescoping matches independently, confirming the pattern used for the full nine-term sum.
So the expression equals 0.99.