Look at this series: 4, 7, 25, 10, __, 20, 16, 19, ... What number should fill the blank?

A. 13 B. 15
C. 20 D. 28

• A.13
  Two series alternate here, with every third number following a different pattern. In the main series, 3 is added to each number to arrive at the next. In the alternating series, 5 is subtracted from each number to arrive at the next.
  
  First series:4,4+3=7,10,10+3=13,16,16+3=19
  Second series:25,25-5=20,20-5=15.
  
• 10 years agoHelpfull: Yes(2) No(0)
• Answer is 13. Seven is three more than 4 as 19 is three more than 16. So 13 is three more than 10.
• 5 years agoHelpfull: Yes(0) No(0)