Look at this series: 21, 9, 21, 11, 21, 13, 21, ... What number should come next?
14
15
21
23

• 15
  
  21, 9, 21, 11, 21, 13, 21, ...15,21,17,21.....
• 12 years agoHelpfull: Yes(4) No(0)
• Ans 13+2 =15
• 9 years agoHelpfull: Yes(0) No(0)
• 15
  In even position the difference between the numbers is 2.
• 7 years agoHelpfull: Yes(0) No(0)
• look at random series then in first series you can observe that only 21 and in the second series leaving one number 9 ,11,13,15
• 6 years agoHelpfull: Yes(0) No(0)
• The answer is 15.The alternate numbers are the odd numbers
• 6 years agoHelpfull: Yes(0) No(0)
• 15
  21 is common between the numbers with the difference of 2
• 5 years agoHelpfull: Yes(0) No(0)
• 21, 9, 21, 9+2, 21, 11+2, 21, 13+2 (15) ans
• 5 years agoHelpfull: Yes(0) No(0)
• every even number is incresaed by 2. so, the answer is 15.
• 5 years agoHelpfull: Yes(0) No(0)
• ans 15
  logic is -12,+12,-10,+10,-8,+18,-6
• 5 years agoHelpfull: Yes(0) No(0)
• 9-21=-12, 21-9=12, 11-21=-10, 21-11=10, 13-21=-8,21-13=8, 15-21=6
  ans=6
• 2 years agoHelpfull: Yes(0) No(0)