Question

The number of numbers lying between 100 and 1000 can be formed with the digit 1,2,3,4,5,6,7

Answer 1

Allowed digits are 1,2,3,4,5,6,7
[Total Digit Count (n) = 7]
Now we have to form three digit numbers using given 7 digits
now hundred's place can be fillled by any of 7 digits as well as, Ten's and Unit's place, so we have total 7*7*7 = 343 numbers

so the answer is 343