Answers

2016-06-19T17:37:20+08:00
One way is finding the absolute value of the difference between terms.

1. 3,12,21,_,_,_

   |3-12| = 9
   |12-21| = 9

As you can see the difference is 9. So the next term would be:

21+9=30
30+9=39
39+9=48

Hope that it helps =)
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