Question:

The number of natural numbers less than $1000$ in which no two digits are repeated is

Updated On: Jul 7, 2022
  • $738$
  • $585$
  • $837$
  • $720$
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The Correct Option is B

Solution and Explanation

Number of one digit natural number $= 9$ Number of two digit natural numbers with different digits $= 9 \times 8$ Number of three digit natural number with different digits $= 9 \times 8 \times 7$ Total number of natural number $
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Notes on Permutations

Concepts Used:

Permutations

A permutation is an arrangement of multiple objects in a particular order taken a few or all at a time. The formula for permutation is as follows:

\(^nP_r = \frac{n!}{(n-r)!}\)

 nPr = permutation

 n = total number of objects

 r = number of objects selected

Types of Permutation

  • Permutation of n different things where repeating is not allowed
  • Permutation of n different things where repeating is allowed
  • Permutation of similar kinds or duplicate objects