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Which term of the AP 3, 15, 27, 39, … will be 132 more than its 54th term?

Class 10Arithmetic ProgressionsAlgebra — Sequences
  • A65
  • B54
  • C60
  • D66

Step-by-Step Solution

d = 12. We need aₙ = a₅₄ + 132. aₙ − a₅₄ = (n − 54)d = 132 → (n − 54)(12) = 132 → n − 54 = 11 → n = 65.
Answer: A) 65

Key idea: n-th term formula

**aₙ = a + (n − 1)d**

Where a is the first term, d is the common difference, n is the position.

**Why**: a₁ = a; a₂ = a + d; a₃ = a + 2d; … aₙ = a + (n − 1)d. Each step adds another d.

**Example**: AP 3, 7, 11, 15, …. Find the 20th term.
a = 3, d = 4. a₂₀ = 3 + 19·4 = 79.

**Reverse use**: 'In the AP 5, 11, 17, …, which term is 89?' a + (n−1)d = 89 → 5 + 6(n−1) = 89 → n = 15.

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