The 12th term and the sim of 1+3+5+7 + ...

To find this, first find the factor or rate of which the numbers are moving. To do so do as follows.

subtract 1 from 3

3-1=2

So each number is having 2 added to it.

Now add two to 7 and the numbers afterwards till you get the 12th term

7+2=9

1+3+5+7+9

9+2=11

1+3+5+7+9+11

11+2=13

1+3+5+7+9+11+13

13+2=15

1+3+5+7+9+11+13+15

15+2=17

1+3+5+7+9+11+13+15+17

17+2=19

1+3+5+7+9+11+13+15+17+19

19+2=21

1+3+5+7+9+11+13+15+17+19+21

21+2=23

1+3+5+7+9+11+13+15+17+19+21+23

So 23 is the 12th term