Engineering Maths - Permutation And Combinations

16. In the above problem, if the first digit cannot be 0, then

  • Option : B
  • Explanation : n=26x 25x 9x 9x 8=421200.
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19. Suppose a licence plate contains two letters followed by three digits with the first digit not zero. How many different licence plates can be printed?

  • Option : C
  • Explanation : Each letter can be printed in twenty-six different ways, the first digit in nine ways and each of the other two digits in ten ways. Hence 26 x 26 x 9 x 10 x 10 = 608400 different plates can be printed.
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20. Given  nPr =  3024

Value of n will be

  • Option : D
  • Explanation : Since is product of consecutive positive integers
    Hence

    npr = 3024 = 9 x 8 x 7 x 6

    Hence,         n = 9

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