11 Answers

31. +1,+2,+3 etc

31. 3+1=4, 4+2=6, 6+3=9…

31

31

31
Source(s): my brain 
31

31
The first number increases by 1 and then the second by 2 and so on. Just add 1 to each previous increase.

31.

The answer is 31…….3,4 is one number added~ 4,6 is two numbers added~6,9 is three numbers added~9,13 is four numbers added~13,18 is five numbers added~18,24 is six numbers added & 24 would have seven added which would make=31

31, 39
add 7, then add 8