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by prernamalhotra » Mon Apr 07, 2014 6:52 am
Hi,

Can you please help me solve the below question:


In how many ways can the letters of the word ABACUS be rearranged such that the vowels always appear together?

A. 6! / 2!

B. 3! * 3!
C. 4! / 2!
D. (4! * 3!) / 2!
E. (3! * 3!) / 2!

Prerna
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Source: — Problem Solving |

by Brent@GMATPrepNow » Mon Apr 07, 2014 7:17 am
prernamalhotra wrote: In how many ways can the letters of the word ABACUS be rearranged such that the vowels always appear together?

A. 6!/2!
B. (3!)(3!)
C. 4!/2!
D. (4!)(3!)/2!
E. (3!)(3!)/2!
Oops, looks like I didn't see the part about the VOWELS APPEARING TOGETHER. I've erased my incorrect solution.

Rather than post a solution similar to Mitch's, I'll just refer you to his solution below.

Cheers,
Brent
Last edited by Brent@GMATPrepNow on Mon Apr 07, 2014 10:35 am, edited 1 time in total.
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by GMATGuruNY » Mon Apr 07, 2014 10:13 am
prernamalhotra wrote:Hi,

Can you please help me solve the below question:


In how many ways can the letters of the word ABACUS be rearranged such that the vowels always appear together?

A. 6! / 2!

B. 3! * 3!
C. 4! / 2!
D. (4! * 3!) / 2!
E. (3! * 3!) / 2!

Prerna
Since the vowels must appear together, put them together in a BLOCK: [AAU].
Now count the number of ways to arrange the 4 elements [AAU], B, C and S.
The number of ways to arrange 4 distinct elements = 4!.

Now we must account for the number of ways that the vowels themselves can be arranged WITHIN the [AAU] block.
The vowels can be arranged as follows:
AAU, AUA, UAA.
Total ways = 3.

Multiplying the results above, we get:
4! * 3.
This is the value yielded by answer choice D:
(4! * 3!)/2! = 4! * 3.

The correct answer is D.
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by sanju09 » Mon Apr 07, 2014 10:55 pm
prernamalhotra wrote:Hi,

Can you please help me solve the below question:


In how many ways can the letters of the word ABACUS be rearranged such that the vowels always appear together?

A. 6! / 2!

B. 3! * 3!
C. 4! / 2!
D. (4! * 3!) / 2!
E. (3! * 3!) / 2!

Prerna
ABACUS has 6 letters in total with 3 vowels AAU occurring in 3 different ways viz AAU, UAA, and AUA. We then have 4 letters to arrange (AAU)BCS if vowels were to emerge together, a total of 4!(3) ways are possible.

Best answer is [spoiler]D[/spoiler]
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