How do I do this using some formula? Looks like a DATA / STATISTICS question!?

Question

a) How many four-digit numbers can you form with the digits 1, 2, 3, 4, 5, 6, and 7 if no digit is repeated?

b) How many of these four-digit numbers are odd numbers?

c) How many of them are even numbers?

Answer 1

a) 7*6*5*4 = 840
b) 480
c) 360

Answer 2

for the first one you can use the formule n!/(n-k)! where n is the number of numbers you have... in this case 7... and k is the number of digits the formed combination must have!

To to find out how many are odd, you need to find out how many end in an odd number and the same with the even ones..

Hope it helps!