Number Series Puzzles - 9

1. What number should replace the question mark ?

    20,21,23,26,?,35.

A:-  30

       20
       20+1 = 21
       21+2 = 23
       23+3 = 26
       26+4 = 30
       30+5 = 35.

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

A:-  15

       21
       21-12 = 9
       9+12  = 21
    
       21-10 = 11
       11+10 = 21
      
      21-8 = 13
      13+8 = 21

     21-6 = 15
     15+6 = 21.

3.  What number should replce the question mark ?

     10,12,16,24,40,72,136,?

A:-  264

       10
       10+2 = 12
       12+4 = 16
       16+8 = 24
       24+16 = 40
       40+32 = 72
       72+64 = 136
       136+128 =264.

4.  Look at this series : 58,52,46,40,34,..... What number should come next ?

A:-  28

      58
      58-6 = 52
      52-6 = 46
      46-6 = 40
      40-6 = 34
      34-6 = 28.