Question

How many 4-digit odd numbers can be formed from the digits 0, 1, 2, 3, 5, 7, 8, if the digits can be repeated?

Answer 1

There are 7 digits: $0,1,2,3,5,7,8.$

There are 4 odd digits among these 7 digits: $1,3,5,7.$

Then $7\cdot7\cdot7\cdot4=1372$ four-digit odd numbers can be formed from the digits 0, 1, 2, 3, 5, 7, 8, if the digits can be repeated.