Example 10 - How many 4-digit numbers can be formed - Chapter 7 - Examples

  1. Chapter 7 Class 11 Permutations and Combinations
  2. Serial order wise
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Example 10(Method 1) How many 4-digit numbers can be formed by using the digits 1 to 9 if repetition of digits is not allowed? n = Numbers from 1 to 9 = 9 r = 4 Required 4 digit number = 9P4 = 9!/((9 − 4)!) = 9!/5! = (9 × 8 × 7 × 6 × 5!)/5! = 3024 Example 10(Method 2) How many 4-digit numbers can be formed by using the digits 1 to 9 if repetition of digits is not allowed? Let the 4 digit number be Number of 4 digit numbers which can be formed = 9 × 8 × 7 × 6 = 3024

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