The citizens of planet nigiet are 5 fingered and have thus developed their decimal system in base 8. A certain street in nigiet contains 1000 (in base 5) buildings numbered 1 to 1000. How many 3s are used in numbering these buildings? Express result in terms of base 10. Choose the correct choice from the following
A) 54
B) 64
C) 75
D) 85
E) 100

Rationale: no of 3 s b / w 1 - 99 is 20,100 - 199 is 20 and so on . so leavn d range b / w 300 - 399 total no of 3 s is ( 9 * 20 = ) 180 . no of 3 s b / w 300 - 399 is ( 20 + 100 = ) 120 . total no of 3 s b / w 1 - 1000 = 120 + 180 = 300 in base 10 300 = 3 * 5 ^ 2 = 75 . answer : c
Answer: C