Find the wrong number in the following series.
10, 21, 43, 85, 175,.....

• 10 21 43 85 175
  
  10*2+1=21
  21*2+1=43
  43*2+1=87
  87*2+1=175
  
  so, 85 is wrong term in series, it should be 87.
• 10 years agoHelpfull: Yes(7) No(1)
• Ans : 85
  
  21 - 10 = 11
  43 - 21 = 22
  so the next diff should be "44"... here the diff is 85 - 43 = 42
  
  So wrong number is 85
• 10 years agoHelpfull: Yes(4) No(0)
• write as (10,21),(43,85),(175,x)
  now for (10,21): 21=10*2+1
  for (43,85): 85=43*-1
  so n*2 +1 then n*2-1 and after then again n*2+1
  x=175*2+1=351
  ans:351
• 10 years agoHelpfull: Yes(0) No(2)
• 10*2+1=21
  21*2+1=43
  43*2+1=87
  87*2+1=175
  so wrong number is 85
• 10 years agoHelpfull: Yes(0) No(0)