Please help my brother with a math problem!

Question

The problem is how many odd digits are there between 140,000 and 170,000 and have no repeated digits? I was trying to help him because I took calculus last year, but I totally forgot how to do this type of problem! Please help me figure out the steps to find the answer. Thank you!

Answer 1

Use some type of a sieve, e.g.,

Start with 30,000 numbers.

Eliminate 44,000's, 55,000's, 66,000's, that is -3,000

Eliminate 45,500's, 56,600's, 67,700's, that is -300

Eliminate 46,600's, 57,700's, 68,800's, that is -300

Continue the process to....