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CMA Foundation · Fundamentals of Business Mathematics and Statistics · Arithmetic Progression and Geometric Progression

A Chennai firm's monthly sales form a GP. Sales in the first month are Rs 2,000 and in the fourth month Rs 16,000. What are the total sales over the first 5 months?

The total sales are Rs 62,000. The common ratio is 2 since r cubed equals 8, and the sum of five terms is 2,000 times 31.

  1. ARs 62,000Correct
  2. BRs 42,000
  3. CRs 32,000
  4. DRs 31,000

Explanation

ar^3 = 16,000 with a = 2,000 gives r^3 = 8, so r = 2. Sum of 5 terms = 2,000 x (2^5 - 1)/(2-1) = 2,000 x 31 = Rs 62,000. Rs 31,000 results from forgetting to multiply by a.

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