hudacse6
In how many ways can the word RAINBOW be arranged so that vowels always come before the consonants?
A. 144
B. 512
C. 720
D. 1440
E. 2880
Take the task of arranging the letters and break it into
stages.
Stage 1: Arrange the 3 vowels (A, I and O) in a row
Property: We can arrange n different objects in n! ways.
So, we can arrange the 3 vowels in 3! ways (= 6 ways)
So, we can complete stage 1 in
6 ways
Stage 2: Arrange the 4 consonants (R, N, B, and W) in a row
So, we can arrange the 4 consonants in 4! ways (= 24 ways)
So, we can complete stage 2 in
24 ways
Stage 3: Place the arrangement of vowels before the arrangement of consonants
We can complete this stage in
1 ways
We're now done arranging all of the letters.
By the Fundamental Counting Principle (FCP), we can complete all 3 stages (and thus arrange the 7 letters) in
(6)(24)(1) ways (= 144 ways)
Answer: A
I'm pretty sure the OA is incorrect.
Note: the FCP can be used to solve the MAJORITY of counting questions on the GMAT. So, be sure to learn it.
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