Hello, MHurricane!

How many f4-digit numbers can you form with the digits 1, 2, 3, 4, 5, 6, 7

a) if no digit is repeated?

There are: . possible 4-digit numbers.

b) How many of these numbers are even?

The last (rightmost) digit has 3 choices: {2, 4, 6}

Choose 3 of the other 6 digits.

. . They can be arranged in: . ways.

Therefore, there are: . even numbers.

c) How many of these numbers are odd?

The rest of them: . odd numbers.