Maths-
General
Easy

Question

How many numbers consisting of 5 digits can be formed in which the digits 3,4 and 7 are used only once and the digit 5 is used twice-

  1. 30    
  2. 60    
  3. 45    
  4. 90    

hintHint:

We know that if there are n objects out of which r are identical ,then
Number of ways of distinct permutations= fraction numerator n factorial over denominator r factorial end fraction

The correct answer is: 60


    To form a 5 digit number with given numbers 3,4,7 (only to be used once) and 5 to be used twice
    We know that if there are n objects out of which r are identical ,then
    Number of ways of distinct permutations= fraction numerator n factorial over denominator r factorial end fraction
    So here, we have 5 digits out of which 2 are identical.
    Number of ways= fraction numerator 5 factorial over denominator 2 factorial end fraction space equals space 60
    Thus, numbers consisting of 5 digits can be formed in which the digits 3,4 and 7 are used only once and the digit 5 is used twice is 60.

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