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10! + 9! can be rewritten as:

This topic has 3 expert replies and 1 member reply

10! + 9! can be rewritten as:

Post
10! + 9! can be rewritten as:

A. 9!(10)
B. 11!/10
C. (10!)^2*9
D. (9!)^2 + 10
E. 19!

OA is B

My approach
10! + 9!
10*9! + 9!
Taking out 9! common
9!(10 + 1)
9!(11)
Now from here i don't know how to proceed. So, i am bit stuck here. However, when i was reviewing, i played around with B
11!/10
(11 * 10 * 9!) / 10
(11)9!
Same outcome as what i got when i solved earlier, but how to get B on my first approach.

Thanks

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GMAT/MBA Expert

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Post
vinni.k wrote:
Brent@GMATPrepNow wrote:
You're almost there!

You have (11)9!
Check the answer choice.....(11)9! isn't there! So, we'll need to check each answer choice.

Thanks Brent,
So, the right approach for this question is to check each of the answer choices.
Once you've rewritten 10! + 9! as (11)9! and discovered that your answer is not among the answer choices, you can EITHER try to rewrite (11)9! so that it matches one of the answer choices, OR you can try to rewrite each answer choice so that it matches (11)9!.
The second option is most likely the faster approach.

Cheers,
Brent

_________________
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GMAT/MBA Expert

Top Reply
Post
vinni.k wrote:
10! + 9! can be rewritten as:

A. 9!(10)
B. 11!/10
C. (10!)^2*9
D. (9!)^2 + 10
E. 19!

OA is B

My approach
10! + 9!
10*9! + 9!
Taking out 9! common
9!(10 + 1)
9!(11)
Now from here i don't know how to proceed. So, i am bit stuck here. However, when i was reviewing, i played around with B
11!/10
(11 * 10 * 9!) / 10
(11)9!
Same outcome as what i got when i solved earlier, but how to get B on my first approach.

Thanks
You're almost there!

You have (11)9!
Check the answer choice.....(11)9! isn't there! So, we'll need to check each answer choice.

A. 9!(10)
We can clearly see that this is not equal to (11)9!
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!)
= B

Cheers,
Brent

_________________
Brent Hanneson – Creator of GMATPrepNow.com
Use our video course along with Beat The GMAT's free 60-Day Study Guide

Sign up for our free Question of the Day emails
And check out all of our free resources

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Post
Brent@GMATPrepNow wrote:
You're almost there!

You have (11)9!
Check the answer choice.....(11)9! isn't there! So, we'll need to check each answer choice.

Thanks Brent,
So, the right approach for this question is to check each of the answer choices.

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Post
vinni.k wrote:
10! + 9! can be rewritten as:

A. 9!(10)
B. 11!/10
C. (10!)^2*9
D. (9!)^2 + 10
E. 19!
10! + 9! = 10 x 9! + 9! = 9!(10 + 1) = 9!(11) = 11!/10

Answer: B

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Jeffrey Miller Head of GMAT Instruction

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