The citizens of planet Oz are 7 fingered and thus have developed an umber system in base 7 . A certain street in Oz contains 100 bvuildings numbered from 1 to 100. how many 3's are used in numbering thers buildings?

15

14

7

21

• the ans is 14. any no from 1 to 100 comes 20 times.so if base is 7 then the maximium no can be 66. the no 37,38,39,73,83,93 will not be counted.and they have six 3's. so total 3's will 20-6=14.
  and ye jo alka h iske ans mat padha karo hamesha galat hoti h.
• 13 years agoHelpfull: Yes(15) No(1)
• for these type of questions,
  the simple formula is (n-1)* (base)^(n-2)
  n=no of digits..
  in this sum, its given as 1 to 100, so for 100 the no of digits is 3
  (3-1)*(7)^(3-2)= 14
  
• 13 years agoHelpfull: Yes(13) No(0)
• more clearly the number between 1 to 100 i base 7 are
  1,2,3,4,5,6
  10,11,12,13,14,15,16
  20,21,22,23,24,25,26
  30,31,32,33,34,35,36
  40,41,42,43,44,45,46
  50,51,52,53,54,55,56
  60,61,62,63,64,65,66
  
  now as the maximum number is 66 and 37,38,39,73,83,93 are not included
  thats why answer is 20-6=14
• 13 years agoHelpfull: Yes(8) No(1)
• 21
  
  1-10---->1
  11-19--->1
  20-->29-->1
  
• 13 years agoHelpfull: Yes(2) No(26)