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📐 Mathematics  ·  Sequences and Series  ·  JEE

The sum 1/(1·2) + 1/(2·3) + ... + 1/(10·11) equals:

Answer: 10/11.

  • A 9/10
  • B 10/11
  • C 11/12
  • D 1

Correct answer: B. 10/11

Explanation: The series telescopes to 1 − 1/(n+1). For n = 10 this is 1 − 1/11 = 10/11.

Each bar grows by the common difference d=3a1=2a2=5a3=8a4=11d=3

Bar heights for AP 2, 5, 8, 11 with the common difference d=3 marked between consecutive terms.

Concept context

Arithmetic progressions, geometric progressions, and sums

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