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





 

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