Official Solution:How many three-digit positive integers have even number of even digits? A. \(100\)
B. \(125\)
C. \(300\)
D. \(325\)
E. \(450\)
We are looking for three-digit positive integers which have zero or two even digits. So, we are looking for three-digit positive integers which have all odd digits or two even digits and one odd digit.
The number of three-digit positive integers with all odd digits is \(5*5*5=125\) (5 odd options for each digit: 1, 3, 5, 7, or 9).
The number of three-digit positive integers with two even digits and one odd digit is a little bit trickier to get. We have to consider two cases:
If the first digit is even (EOE or EEO), then there will be \(4*5*5+4*5*5=200\) numbers (4 even options for the first digit: 2, 4, 6, or 8 because a three-digit number cannot start with 0).
If the first digit is NOT even (OEE), then there will be \(5*5*5=125\) numbers.
The total number of such numbers is therefore, \(125+200+125=450\)
Answer: E