Hello, Faisal2007!

How many 4-digit numbers can you form with (1,2,3,4,5,6,7) ?

(No repeated numbers)

The answer is: .

But how many of these are odd numbers?

The last (rightmost) digit must be odd; there are choices: 1, 3, 5, or 7.

The other three digits are chosen from the remaining six digits: . ways.

Therefore, there are: . odd numbers.