CMA Foundation · Fundamentals of Business Mathematics and Statistics · Arithmetic Progression and Geometric Progression
Three numbers are in GP with a first term of 4 and a last term of 36. What is the geometric mean inserted between them, taken as positive?
The positive geometric mean is 12. The middle term of a three-term GP equals the square root of the product of the first and last terms, which is the square root of 4 times 36, or 144. This gives 12, whereas 20 is the arithmetic mean.
- A20
- B12Correct
- C16
- D9
Explanation
The middle term of three GP terms is the square root of the product of the extremes: sqrt(4 x 36) = sqrt(144) = 12. Option 20 is the arithmetic mean (4+36)/2, which is a different mean.
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