Calculating Geometric Mean Annual Increase: Cable TV Subscribers 1990-2000

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Discussion Overview

The discussion revolves around calculating the geometric mean annual increase in cable TV subscribers from 1990 to 2000, with specific focus on the numbers of subscribers and the interpretation of annual increase versus percentage increase.

Discussion Character

  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant proposes that the geometric mean annual increase can be calculated as (9.19*54.87)^(1/2) = 22.46 million, but seeks confirmation on this approach.
  • Another participant argues that the first calculation is incorrect as it averages the number of viewers rather than calculating the annual increase.
  • A different participant suggests that the annual increase can be derived from the equation 9.19 * x^10 = 54.87, leading to an annual percentage increase of approximately 19.56%.
  • One participant clarifies that the arithmetic mean annual increase is 4.569 million, contrasting it with the percentage increase, indicating a misunderstanding in terminology.
  • Another participant emphasizes that the ratio of the number of subscribers in 2000 to those in 1990 should be taken to find the annual increase, suggesting a method without performing the arithmetic.
  • There is a reiteration that the 19.56% figure refers to the annual percentage increase, not the annual increase itself.

Areas of Agreement / Disagreement

Participants disagree on the correct interpretation of "annual increase" versus "annual percentage increase," with no consensus reached on the correct method for calculating the geometric mean annual increase.

Contextual Notes

There is a lack of clarity regarding the definitions of "annual increase" and "annual percentage increase," which contributes to the confusion in the discussion. The mathematical steps for deriving the geometric mean annual increase remain unresolved.

PARAJON
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I have a question that I would like your assistance to see if I have the correct info:


In 1990 there were 9.19 million cable TV subscribers. By 2000 the number of subscribers increased to 54.87 million. What is the geometric mean annual increase for the period ?


Answer:

(9.19*54.87)^(1/2) = 22.46 million


I would appreciate your help in this matter to come up with the correct answer.

I also have another possible answer of 19.56%


Thank you!
 
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Neither of those answers has any hope of being correct.

In the first case, "(9.19*54.87)^(1/2) = 22.46 million" you are averaging the number of viewers, not the annual increase in the number of viewers.
In the second case, you have a percentage and the problem asks for "annual increase" not percentage annual increase.

IF the problem had asked for "arithmetic" mean (or just "mean") it would be easy: the total increase from 1990 to 2000 is 54.87- 9.19= 45.68 million which would be a mean annual increase for those 10 years of 45.68/10= 4.569 million.

Letting a1, a2, ... , an, be the actual annual increase, you want a number a such that a1*a2*...*a10= a10 AND a1+ ...+ a10= 45.68. Since sums and products don't combine nicely, I don't see any way of getting that.
 
the 19.56% answer is the annual increase.

9.19 * x^10 = 54.87
x = (54.87/9.19)^(1/10)

which is 1.195644 ~ 19.56%.

22.46 is the geometric mean of 9.19 and 54.87 but i don't see how that is important here.
 
Take the ratio (R) of no. of 2000 over no. in 1990. The answer you want is R1/10. I'll let you do the arithmetic.
 
"the 19.56% answer is the annual increase."

No, it's the annual percentage increase. The (arithmetic) mean annual increase is 4.569 million as I said. There's a big difference.

"Take the ratio (R) of no. of 2000 over no. in 1990. The answer you want is R1/10. I'll let you do the arithmetic."
That is 1.1956= "1+r" where r is the annual percentage increase. I don't see how that could be called the "geometric mean annual increase".
 
HallsofIvy said:
No, it's the annual percentage increase.

you are right, of course :)
 

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