In the following sum, “?”, stands for which digit?
? + 1? + 2? + 3? + ?1 = 21?

• I think your question is wrong.
  
  The correct question is
  ? + 1? + 2? + ?3 + ?1 = 21?
  
  Ans : 8
  
• 10 years agoHelpfull: Yes(18) No(2)
• let the digit be x. so the series becomes:
  x + (10 + x) + (20 + x) + (30 + x) + (10x + 1)=210 + x
  => 14x + 61 = 210 + x
  => 13x = 149
  =>x = 149/13 = 11.46 (i don't think the answer is correct!)
• 11 years agoHelpfull: Yes(4) No(9)
• question wrong..it should be ?3
• 9 years agoHelpfull: Yes(2) No(0)
• let x be the ? .
  then by applying,we get
  1+(1*x)+(2*x)+(3*x)+(1*x)=21
  7x+1=21
  7x=20
  x=20/7
  x=2.85
  
• 10 years agoHelpfull: Yes(1) No(6)
• The question is which digit can replace the question mark
  ?+1?+2?+?3+?1=21?
  None of these
  5
  7
  8
  ANS is 8
  8+18+28+83+81=218
  Replace '?' by 8
  The question copied here is wrong, if the queston mark is after 3. No digit can replace the question mark. Check it out!
• 6 years agoHelpfull: Yes(1) No(0)