Arithmatical - Permutations and Combinations

DIRECTIONS : Problems based on Permutations.
21. In how many different ways can the letters of the word 'SOFTWARE' be arranged in such a way that the vowels always come together?
  A.  720
  B.  360
  C.  1440
  D.  13440
Solution
The word 'SOFTWARE' contains 8 letters.
When the vowels OAE are always together, they can be supported to form one letter.
Thus, we have to arrange the letters SFTWR (OAE).
Now, 5 letters can be arranged in 6! = 720 ways.
The vowels (OAE) can be arranged among themselves
in 3! = 6 ways.
Therefore required number of ways= (720 x 6)
= 4320.

22. Find the value of 10C3
  A.  30
  B.  60
  C.  90
  D.  120
Solution
10C3= 10 x 9 x 8 / 3!
= 10 x 9 x 8 / 3 x 2 x 1
= 120.
23. In how many different ways can the letters of the word ‘LEADING’ be arranged in such a way that the vowels always come together?
  A.  360
  B.  480
  C.  530
  D.  720
Solution
The word 'LEADING' contains 7 letters.
When the vowels EAI are always together, they can be supported to form one letter.
Then, we have to arrange the letters LDNG (EAI).
Now, 5 letters can be arranged in 5! = 120 ways.
The vowels (EAI) can be arranged among themselves
in 3! = 6 ways.
Therefore required number of ways= (120 x 6)
= 720.
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