how many 3 digit numbers can be formed using the digits 0,1,2,3,4,5,6, if repitition is not allowed?

Answer 1

assuming no leading zeros, there would be

6 * 6 * 5

candidates.

Answer 2

Since starting with 0 would not make it a 3-digit number, we have only 6 choices for the lead digit

so number of cases
= 6 x 6 x 5
= 180