A geometric sequence has first term 1 and common ratio 5. Find the sum of its first 4 terms.

Answer and explanation

Correct answer: B. 156

  1. Step 1: Use S_n = a(r^n - 1)/(r - 1) for r not equal to 1.
  2. Step 2: S = 1(5^4 - 1)/(5 - 1) = 1 x 624 / 4 = 156.
Answer
156.
Why not the others: '125' gives the last term instead of the sum; '625' gives the (n+1)th term; '157' adds the first term twice.

Practise more Algebra, Functions, Geometry and Probability.

Free questions with an explanation for every one, and full timed Državna Matura (Bosnia & Herzegovina) mock tests.

All Algebra, Functions, Geometry and Probability questionsTake a mock test

More Algebra, Functions, Geometry and Probability questions