How many natural numbers less than 1000 can be formed from the digits 0,1,2,3,4,5 when a digit may be repeated any number of time?

Number of 1-digit numbers = 5 (0 can't be used)

Number of 2 digit numbers = 5 × 6 = 30 (0 can't be used at tens place)

Number of 3 digit numbers = 5 × 6 × 6 = 180 (0 can't be used at hundreds place)

∴Total numbers = 5 + 30 + 180 = 215

Cheers!!!

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