not sure if you have learned how to use AP to tackle this qns.
2 4 6 8
For numbers starting with 2, we have 2, (20-29) , (200-299), (2000-2999), (20000-29999)
same for 4 6 and 8
For odd # starting with 2 :
For 2,
0
For 20-29,
1st odd term is 21 , d is 2, last term is 29...