A probability question

[languid night]

We construct 4-digit numbers, which are chosen from any of the following seven digits: 0, 1, 3, 5, 7, 8, 9. Answer the following:
a) How many different numbers are possible if a digit can be used more than once?
b) How many different numbers are there that contain no identical digits?
c) What is the probability of a number having no digit ‘7’ and containing two or more identical digits?
How do you do question C

[bronze hollow]

Ok fist think about the probability for the first number, because you can get 6 out of the 7 numbers it should be 6/7

[thick aspen]

Why 6 out of 7? I don't think this is right. Or maybe you're not answering the question I think you're answering.

[bronze hollow]

For c?

for the first digit, it can be 0,1,3,5,8,9 six numbers

and there are 7 available

so 6/7

correct me if im wrong

oh the probability doesnt change sorry

[thick aspen]

The question is a little vague, but usually a 4-digit number can't have a 0 in the thousands place.