The number of natural numbers less than 500 in which no two digits are repeated is

The number of natural numbers less than 500 in which no two digits are repeated is
  1. $374$
  2. $376$
  3. $378$
  4. $380$

Solution

Number of 3 digit natural number less than 500 in which no two digits are repeated $=4 \times 9 \times 8=288$
4 ways $=4$ number $(1,2,3,4)$ Now number of 2 digit natural numbers less than 500 in which no. of two digits are repeated $=9 \times 9=81$ Now number of 1 digit natural number less than $500=9$ Therefore required number of digits $=288+81+9=378$

Asked in: AP EAMCET 2023 (19 May Shift 1)

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