How many 7’s are there between 0 to 400?

• If u mean
  
  How many 7s are there between 0 to 400?
  
  From 0 to 100, there are 20 sevens.
  7,17,27,37,47,57,67,70,71,72,73,74,75,76,77,78,79,87,97
  
  From 0 to 400, there are 4*20 = 80 sevens.
• 12 years agoHelpfull: Yes(67) No(20)
• Let us consider a general number (100A+10B+C)
  Now, by problem A=0,1,2,3.
  Now, consider the following cases:
  1st case: WHEN B = 7 BUT C IS NOT EQUAL TO 7:
  ------------------------------------------------------
  In this case A=0,1,2,3.
  C=0,1,2,3,4,5,6,8,9.
  So,in this case a total number= 4*9=45;
  
  2nd Case: WHEN C = 7 BUT B IS NOT EQUAL TO 7:
  --------------------------------------------------------
  Now, also A=0,1,2,3
  B=0,1,2,3,4,5,6,8,9
  So, here also 4*9 = 36 cases.
  
  So, for both the above cases
  We get a total (36+36)=72 numbers each containing a 7 as one of its digits.
  
  Now, 3rd Case : When B=7 & C=7:
  -------------------------------------------
  In this case A=0,1,2,3
  B=7
  C=7
  So, total number of integers = 4
  Now,note that in this case every integer contains two 7 [since B=C=7] .
  So, total number of 7 in this 3rd case = 2*4 =8.
  
  Now, clearly none of the above 3 cases ,overlaps with each other.
  
  So, from 0 ----> 400 ,we get a total of (36+36+8)= 80 sevens..
  
  So, 80 sevens are there between 0 to 400..
  
  Thanks to all..:-):-)..
  
• 12 years agoHelpfull: Yes(30) No(10)
• every 0-100 there are 9+10 sevens
  9 for 0-67,80-100,
  10 is for 70-79
  so totally 19sevens/100
  using this for 400=19*4=76 sevens only
  76
• 12 years agoHelpfull: Yes(11) No(42)
• Please mention the problem properly & clearly..
• 12 years agoHelpfull: Yes(5) No(4)
• ans is 80. O-100 there are 20 7's accordind to this there are 80 7's between 0-400.
• 12 years agoHelpfull: Yes(5) No(7)
• first find between 0 to 100,
  it can be written as 00,01,02,03,......to 99... bcz, 100 do not have any 7's and it do not affect the number of 7's.... hence the total number of digits in 00 to 99 are 200.... consisting of 0 to 9 digits.. hence 200/10 = 20 digits of each type....( 0,1,2,3,4,5,6,7,8,9) hence 20 number of 7's.
  similarly, from 100 to 200, - 20 7's
  200 to 300 - 20
  300 to 400 - 20
  total= 80.
• 12 years agoHelpfull: Yes(5) No(6)
• in 1 to 100 thr r 20 7's ( any of 2 3 4 5 6 7 8 9)
  so 0-400 80 7's
• 12 years agoHelpfull: Yes(2) No(1)
• 400/7+400/49+400/343
  57+8+1=66
  
  value/n+value/n square+value/n cube 66 ans
• 11 years agoHelpfull: Yes(2) No(0)