Consider digits 1,2,3,4,5,6 and 7. Using these digits, numbers of five digits are formed. Then, probability of these such five digit numbers that have odd digits at their both ends only, is(repetition not allowed)
A
37
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B
17
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C
27
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D
None of these
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Solution
The correct option is C27 The given statement says that 5 digit numbers are made from 7 digits.
The probability of selecting 5 digits from 7 is given by 7P5
The odd numbers are 4 in number and thus 2 of them can be selected by 4P2 and the remaining three from the even numbers as 3P3
Thus the probability is given by : (4P2 x 3P3)/(7P5) =27