It is with great sorrow that Ikleyn does not know that numerical reasoning
tests for employment nearly always contain many sequences just like this one.
3, -6, 12, 4, 20, ? which number comes next
We look at the sequence of differences:
3 -6 12 4 20
-9 18 -8 16
The sequence of differences looks like it's going like this
-9 18 -8 16 -7 14 -6 12 -5 10 -4 8 ...
where the odd terms are going -9, -8, -7, -6, -5, -4,...
and the even terms are going 18, 16, 14, 12, 10, 8,...
So to get the next term of
3, -6, 12, 4, 20,
We stick a -7 on the sequence of differences:
3 -6 12 4 20
-9 18 -8 16 -7
Then we add the 20 and the -7 to get the next term:
3 -6 12 4 20 13
-9 18 -8 16 -7
which is 13.
Edwin
