If o represents number of integers between 10,000 and 100,000 all of whose digits are odd, and e represents number of integers between 10,000 and 100,000 all of whose digits are even, what is the value of o - e?

I) 
fist let's find O, that is the number of all numbers between 10,000 and 100,000, whose all digits are odd.

so we have to count: 11,111;       11,113;       ... 99,999

we notice that all these numbers are 5 digit, and they are made up of the odd digits {1, 3, 5, 7, 9} with repetition allowed.

so there are in total  such numbers.

ii) 

E is the total number, of 5-digit numbers formed from the set{0, 2, 4, 6, 8} with repetition allowed, and the first digit not equal to 0.

so 

iii) 

625