Bunuel wrote:
10! + 9! can be rewritten as:
A. 9!(10)
B. 11!/10
C. (10!)^2*9
D. (9!)^2 + 10
E. 19!
First recognize that 10! = (10)(9!)
Here's why:
10! = (10)
(9)(8)(7)(6)(5)(4)(3)(2)(1)= (10)
(9!)So....
10! + 9! = (10)(9!) + 9!
= 9!(10 + 1)
[I factored out the 9!]= 9!(11)
Check the answer choice.....9!(11) isn't there! So, we'll need to check each answer choice to see which one can be expressed as (9!)(11)
A. 9!(10)
We can clearly see that this is not equal to (9!)(11)
ELIMINATE A
B. 11!/10
11!/10 = (11)(
10)(9)(8)(7)(6)(5)(4)(3)(2)(1)/(
10)
= (11)
(9)(8)(7)(6)(5)(4)(3)(2)(1)= (11)
(9!) PERFECT!!
= B
Cheers,
Brent
_________________
Brent Hanneson – Creator of gmatprepnow.com
I’ve spent the last 20 years helping students overcome their difficulties with GMAT math, and the biggest thing I’ve learned is…
Many students fail to maximize their quant score NOT because they lack the skills to solve certain questions but because they don’t understand what the GMAT is truly testing -
Learn more