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#1 2021-04-17 08:50:53

mathland
Member
Registered: 2021-03-25
Posts: 444

Primate Reserve

At a primate reserve, the mean age of all the male primates is 15 years, and the mean age of all female primates is 19 years. Which of the following must be true about the mean age m of the combined group of male and female primates at the primate reserve?

1. m = 15 + 19

2. m > 15 and less than 20.

3. 15 < m < 19

4. None of the above.

Let me see.

I say the answer is choice 3. Of course, this is just my guess.
If I am right, what makes choice 3 correct?

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#2 2021-04-17 19:11:29

Bob
Administrator
Registered: 2010-06-20
Posts: 10,053

Re: Primate Reserve

I think that's correct.  The female result will pull up the overall average compared with male alone and the male result will pull down the overall compared with the female alone.

I'd do some algebra here.

Lets say there are M males and F females.

Then we know that total males = 15M and the total females = 19F.

So the overall average = (15M + 19F)/(M+F)

(15M + 15F)/(M+F) < (15M + 19F)/(M+F) < (19M + 19F)/(M+F)

15 < (15M + 19F)/(M+F) < 19

Bob


Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob smile

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#3 2021-04-18 06:12:55

mathland
Member
Registered: 2021-03-25
Posts: 444

Re: Primate Reserve

Bob wrote:

I think that's correct.  The female result will pull up the overall average compared with male alone and the male result will pull down the overall compared with the female alone.

I'd do some algebra here.

Lets say there are M males and F females.

Then we know that total males = 15M and the total females = 19F.

So the overall average = (15M + 19F)/(M+F)

(15M + 15F)/(M+F) < (15M + 19F)/(M+F) < (19M + 19F)/(M+F)

15 < (15M + 19F)/(M+F) < 19

Bob

I guess I was right.

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