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How do i solve this question?

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Re: How do i solve this question?

by Stuart@KaplanGMAT » Thu Jan 31, 2008 12:54 pm
Anntaylor wrote:81!* 80!
_______ = ?
79!

let me know how you solve this, if possible, thanks..
With a very big calculator!

We know that 80! = 80*79*78*77*...*1 = 80*79!

So, the quickest way to simplify is:

(81!)(80!)/(79!) = 81!(80*79!)/79! = 81!(80)

There are other variations we could get, but the answer probably looks something like mine.

If the answer choices look radically different, please post them. On a multiple choice test like the GMAT, a great first step is to check the choices to gain some insight into what exactly the question is testing.
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re

by Anntaylor » Fri Feb 01, 2008 9:23 am
the answer is 4 digit number

options were

1) 4 digit number

2) 4 digit number

3) 4 digit number

4) 4 digit number

5) 4 digit number..


all starting with 6... so it was 6 thousand something..

and 81! * 80 .. is way more than 4 digits..

lemme know if anyone can come up with an answer..
i cant figure out how this is possible
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Re: re

by Stuart@KaplanGMAT » Fri Feb 01, 2008 11:01 am
Anntaylor wrote:the answer is 4 digit number

options were

1) 4 digit number

2) 4 digit number

3) 4 digit number

4) 4 digit number

5) 4 digit number..


all starting with 6... so it was 6 thousand something..

and 81! * 80 .. is way more than 4 digits..

lemme know if anyone can come up with an answer..
i cant figure out how this is possible
If the answer is a 4 digit number, then the question is misquoted.

Could the question have been:

(81*80!)/79!?

That would give us 81*80, which would be a bit more than 6400 (80^2).
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