3, 12, 7, 26, 15, ?
a)54 b)27 c)108 d)31

• answer is:54
  one of the series is 12,26,54
  12*2=24+2=26;
  26*2=52+2=54;
• 13 years agoHelpfull: Yes(9) No(0)
• there are two series
  3
  12
  7 = 3*2+1
  26 = 12*2+2
  15 = 7*2+1
  26*2+2 =54
• 13 years agoHelpfull: Yes(6) No(0)
• 12*2+2=26
  26*2+2=54
• 10 years agoHelpfull: Yes(1) No(0)
• 3 , 12, 3*2+1 , 12*2+2 , 7*2 + 1 , 26*2 + 2
  therefore , a)54
• 8 years agoHelpfull: Yes(0) No(0)