GMAT PREP ?? (ARITHMETIC MEAN)

dferm · Posted: Wed May 07, 2008 10:32 am Post subject: GMAT PREP ?? (ARITHMETIC MEAN)

What is the average (arithmetic mean) of eleven consecutive integers?

(1) The average of the first nine integers is 7
(2) The average of the last nine integers is 9

Can someone put a little light on this prob?

Thanks.

rlemaire · Posted: Wed May 07, 2008 11:30 am Post subject: GMAT Prep?? MEAN

I am not totally sure that I am 100% completely right (you might want to double check) but this is how I view the question you posted below.....

What is the average (arithmetic mean) of eleven consecutive integers?

(1) The average of the first nine integers is 7
(2) The average of the last nine integers is 9

Can someone put a little light on this prob?

To find the Arithmetic Mean of 11 consecutive integers you must view Number 1 to start.

Number 1 tells us that the average of the "first 9" of our consecutive integers must equal 11. I first used integers 1 - 11 but found that when I averaged 1 - 9 I came up to only 6 (Arithmetic Mean). Same thing with 2 - 12 with average of 6. So I tried 3 - 13 and found that the average of 3, 4, 5, 6 , 7, 8, 9, 10, and 11 averaged 7.

I checked this against the second set to see if the average was 9. So, 5, 6, 7, 8, 9, 10, 11, 12, and 13 equal the average of 9 that we are looking for.

There is still one more step and that is to average the 3 - 13. That came out to be 8.

So your answer, as I see it, is 8 and you must use 3 - 13 to get it.

If you want the excel version of what I did then email me and I can upload it.

Hope this helps!!!!!

Stuart Kovinsky