when a certain number 'X' is multiplied by 18, the product 'y' has all digits as 4s. What is the minimum number of digits 'X' can have?

(a)8
(b)9
(c)12
(d)18

• by verification: (12345679)*9= 111111111
  (12345679)*18=222222222
  and in the same way(12345679)*36=444444444
  so the num multiplied with 18 to get all 4 digits is
  =(12345679)*2*18=24691328*18
  =444444444
  so the minimum no of digits x can have are 8 digits
  
• 11 years agoHelpfull: Yes(29) No(7)
• X*18=Y (having all 4s
  Digit on R.H.S. must be divisible by 18 or must be divisible by p
  So, considered a condition that satisfy RHS (divisible by 9 and having all 4s)
  The only situation will be 9 times 4 i.e. 444444444
  So when 444444444 divided by 18 it gives 24691358 (having 8 digits)
• 11 years agoHelpfull: Yes(6) No(3)
• x*18=444...
  x=(444...)/18
  x=(222...)/9
  any no is divisible by 9 only when sum of all its digits is divisible by 9
  so
  2+2+2..9 times=18 which is divisible by 9
  so, x=222222222/9=24691358, which has 8 digits.
  Answer=8
• 10 years agoHelpfull: Yes(6) No(0)
• from where did u get the nos. 12345679 ???
• 11 years agoHelpfull: Yes(3) No(0)
• b-9 digits is exactly correct , the reason is x*18 = 44444...,so here the number
  x = 4444444...../18.so 44444... should be divisible by 18,so it should be divisible by both 2 and 9.as last digit is 4 so divisible by 2 ok,but it should contain 9 fours to be divisible by 9. see 444444444(sum of digits = 36-divisible by 9).
• 11 years agoHelpfull: Yes(3) No(0)
• X*18=Y (having all 4s
  Digit on R.H.S. must be divisible by 18 or must be divisible by 9
  So, considered a condition that satisfy RHS (divisible by 9 and having all 4s)
  The only situation will be 9 times 4 i.e. 444444444
  So when 444444444 divided by 18 it gives 24691358 (having 8 digits)
• 11 years agoHelpfull: Yes(2) No(1)