Permutation and CombinationHard
Question
The number of permutations which can be formed out of the letters of the word ″SERIES″ taking three letters together, is:
Options
A.120
B.60
C.42
D.none
Solution
SERIES
S - 2, E - 2 , R, I
case-I when all letter distinct is
4C3 × 13 = 4 × 6 = 24
case-II when 2 letters are same the
2C1 . 3C1 ×
= 2 . 3 . 3 = 18
total number is 24 + 18 = 42
S - 2, E - 2 , R, I
case-I when all letter distinct is
4C3 × 13 = 4 × 6 = 24
case-II when 2 letters are same the
2C1 . 3C1 ×
= 2 . 3 . 3 = 18total number is 24 + 18 = 42
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