Quantrex Quantrex AcademyJEE · NEET · NDA PYQs with solutions Open app
NDA2014MathematicsSequences and SeriesActual

Let S _n denote the sum of first n terms of an AP and 3 ~S _n= S _ 2 n . What is S _ 3 n : S _ 2 n equal to ?

Options

  1. A2: 1
  2. B3: 1
  3. C4: 1
  4. D5: 1

Correct answer

A. 2: 1

Step-by-step solution

S_ 3 n S_ 2 n = 3[2 a+(3 n-1) d] 2[2 a+(2 n-1) d] aligned & = 3 2 [ n d+d+3 n d-d n d+d+2 n d-d ]= 3 2 4 3 =2 ~S _ 3 n : S _ 2 n & =2: 1 . aligned

Practice Sequences and Series on Quantrex Academy →

More from Sequences and Series

Let p , q and r be three unequal numbers such that p , q and r are in AP. If (q-p) , (r-q) and p are in GP, then (p+q):(q+r):(r+p) equals 2026If p^ th term of an AP is k , then what is the sum of p^ th term, (p+q)^ th term and (p-q)^ th term of the AP ? 2026If p , g₁ , g₂ and q are in GP and m is the arithmetic mean of p and q , then g₁^2 g₂ + g₂^2 g₁ is equal to 2026The sum of the first n terms of an AP is 3n^2+5n . If the m^ th term of the AP is 68 , then what is the value of m ? 2026Passage: Let X(a,p) , Y(b,q) and Z(c,r) be the points such that a , b and c are in AP. Question: If p , q and r are not in AP and b=c , then the line joining the points X , Y and Z 2026If (10 + ₁₀ x) , (10 + ₁₀ y) and (10 + ₁₀ z) are in AP, then consider the following statements: I. The GM of x and z is y^2 . II. The AM of ₁₀ x and ₁₀ z is ₁₀ y . Which of the sta 2025How many terms of the series 1 + 3 + 5 + 7 + amount to a sum equal to 12345678987654321 ? 2025For the following two (02) items: Let (6 + 10 + 14 + up to m terms ) = (1 + 3 + 5 + 7 + up to n terms ) , where m How many values of m are possible? 2025 Full Sequences and Series list All NDA PYQs