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Re: If ¡n! = (n!)^2, then ¡17! - ¡16! = [#permalink]
Bunuel, can you please tell if factorial questions are asked in GMAT? Thanks!!
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Re: If ¡n! = (n!)^2, then ¡17! - ¡16! = [#permalink]
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PareshGmat wrote:
Bunuel, can you please tell if factorial questions are asked in GMAT? Thanks!!


Yes, most definitely. I'd suggest you to go through Official Guide to know the concepts tested on the GMAT.
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Re: If ¡n! = (n!)^2, then ¡17! - ¡16! = [#permalink]
J17! = 17! * 17!
THIS can be rewritten as: 16! * 17 * 16! * 17.

now, 16! * 16! is j16!.

we can factor out j16!
we are left with j16! (17*17 - 1) = j16! * 288
288=144 *2 or 12^2 * 2.
answer E.
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Re: If ¡n! = (n!)^2, then ¡17! - ¡16! = [#permalink]
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Can someone tell me why you subtract the 1 when you're factoring out 16!
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Re: If ¡n! = (n!)^2, then ¡17! - ¡16! = [#permalink]
Can someone explain me why D is not correct, I can't get it: the only difference in (17!)^2 and (16!)^2 isn't just the 17^2??
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Re: If ¡n! = (n!)^2, then ¡17! - ¡16! = [#permalink]
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Fedemaravilla wrote:
Can someone explain me why D is not correct, I can't get it: the only difference in (17!)^2 and (16!)^2 isn't just the 17^2??


No. \((17!)^2 - (16!)^2 = 126075783368849775132672000000\) not 17^2
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Re: If ¡n! = (n!)^2, then ¡17! - ¡16! = [#permalink]
Not sure why we subtract the 1 can someone help Bunuel
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Re: If ¡n! = (n!)^2, then ¡17! - ¡16! = [#permalink]
¡n! = (n!)^2
¡17! - ¡16!

(17!)^2 - (16!)^2

(17! * 17!) - (16! * 16!)

Can be written as
17*16! *17* 16! -16! *16!
Taking common
16!*16! (17*17 -1)

(16!)^2 (289-1)

¡16!(288)

E

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Re: If ¡n! = (n!)^2, then ¡17! - ¡16! = [#permalink]
Did a different way and got a wrong result - Pls help

(17!)^2 - (16!)^2
(17! + 16!) * (17! - 16!)
16!(17+1) * 16! (17-1)
16!*16!*18*16
2*16!*18*16, which is 2 times the right answer choice.
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If ¡n! = (n!)^2, then ¡17! - ¡16! = [#permalink]
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cptholt wrote:
Did a different way and got a wrong result - Pls help

(17!)^2 - (16!)^2
(17! + 16!) * (17! - 16!)
16!(17+1) * 16! (17-1)
16!*16!*18*16
2*16!*18*16, which is 2 times the right answer choice.


16!*16!*18*16 is (16!)^2 * 288
Its 16!*16! not 16!+16!

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Re: If ¡n! = (n!)^2, then ¡17! - ¡16! = [#permalink]
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