how many three digit number are thre in which if one digit is 3 then it must be follwed by 7 . repetetion is not allowed
a 466
b 463
c 14
d 17

• answer is 463
  solution: 1st case: three digits no without considering 3
  first place can be filled using 8 numbers (excluding 0 and 3)=8
  second place can be filled using 8 numbers (excluding 3 and digit filled in first place)=8
  last place can be filled using 7 numbers (excluding 3 and digit filled in first place & second place)=7
  therefore, three digits formed are= 8*8*7=448
  
  2nd case: now consider number using 3
  if 3 and 7 are first two digit then last digit can be filled using 8 digits
  if 3 and 7 are last two digits then first place can be filled using 7 digits
  therefore, total 3 digit no including 3 are= 8+7=15
  
  hence, total 3 digits numbers are= 448+15=463
• 8 years agoHelpfull: Yes(29) No(6)
• Ans - b) 463
  The question says that if one number is 3 then it must be followed by 7, It does not says that we must include 3 in our formation of three digit number. Thus,
  Let's count the number of three digit numbers without having 3 in it -
  i.e. 8 x 8 x 7 = 448
  
  Now, let's count the number of three digit numbers having 3 in it and is followed by 7 -
  This would include two arrangements -
  1) 37_ (Total 8 arrangements can be done i.e. 370, 371, 372, 374, 375, 376, 378, 379).
  
  2) _37 (Total 7 arrangements can be done i.e. 137, 237, 437, 537, 637, 837, 937).
  
  Hence, total number of three digit numbers can be formed is 448+8+7 = 463.
• 7 years agoHelpfull: Yes(4) No(0)
• ans : will be 14 as If 3 and 7 will be last 2 digits then first digits will be filled by 7 digits and same if 3 and 7 are first 2 digits
• 8 years agoHelpfull: Yes(2) No(14)
• Yup ans is 463..
  As we have to take ths case whn 3 is not there
  Nd one case when if 3 comes thn it will be followed by 7
• 8 years agoHelpfull: Yes(2) No(2)