Question 11166
you have

1, 2, 3, 4, 5, 6, 7, 8, 9, 10
and
3, 5, 7, 9, ............... ?


well, you can work them all out, as follows:
3, 5, 7, 9, 11, 13, 15, 17, 19, 21


so answer is 21


or you can find the "pattern" or the "equation" of this sequence.
Look at the 3, 5, 7, 9 etc.. it is just the 2 times table, yes? moved a bit... the DIFFERENCE between the numbers is 2.


So, calling the top line of numbers n, the bottom line of numbers is defined as 2n. But hang on, 2n gives the wrong answers, as shown here:


n = 1, 2, 3, 4,...
2n= 2, 4, 6, 8,...

we want
? = 3, 5, 7, 9,...


so, basically we just need to add 1, giving 2n+1. This is the rule that explains the numbers.


So, for the tenth term, n=10, we have 2n+1 which gives (2*10) + 1 --> 20 + 1 --> 21.


Does that helps?


Jon.