4, 2, 5, 9, 5, 11, 13, 7, 16, 17, 9

• ans is 21
  5-4=1
  11-9=2
  16-13=3
  21-17=4
• 11 years agoHelpfull: Yes(19) No(2)
• 
  
  
  
  
  (4,9,13,17),(2,5,7,9),(5,11,16,x)
  x=21
  
  
  
• 11 years agoHelpfull: Yes(17) No(7)
• (4,2,5)(9,5,11)(13,7,16)(17,9,?)
  4+2=6/2=3+2=5
  9+5=14/2=7+4=11
  13+7=20/2=10+6=16
  17+9=26/2=13+8=21
• 11 years agoHelpfull: Yes(6) No(0)
• (4,2,5),(9,5,11),(13,7,16)),(17,9,?)
  5-4=1*1+1=2
  11-9=2*2+1=5
  16-13=3*2+1=7
  21-17=4*2+1=9
• 11 years agoHelpfull: Yes(2) No(1)
• ANS:21
  (4 , 4-2=2 , 2+3=5)
  (9 , 9-4=5 , 5+6=11)
  (13, 13-6=7 , 7+9=16)
  (17, 17-8=9, 9+X=21)
  X=12
  SO ANS IS 21.
• 11 years agoHelpfull: Yes(2) No(1)
• 4+2-1=5
  9+5 -3=11
  17+3 -4=16
  17+9-7=19
  
• 11 years agoHelpfull: Yes(1) No(4)