The first things we notice about this number series are
- that each number is greater than the one preceding it
- that the intervals between the numbers vary
- and that none of the numbers is a multiple of the one preceding it.
On the basis of this initial assessment, we can already arrive at a few assumptions about the rule: A different number is added in each case.
The next step is to determine which number is added in each case.
We get from 60 to 66 by adding 6.
We get from 66 to 96 by adding 30.
We get from 96 to 100 by adding 4.
We get from 100 to 120 by adding 20.
We get from 120 to 122 by adding 2.
Now a rule can be discerned: The first, third and fifth of the numbers added (6, 4 and 2) and the second and fourth of the numbers added (30 and 20) can be more easily associated with one another than any of these added numbers with the one immediately preceding or succeeding it. In the first group, each number is obtained by subtracting 2 from the preceding number; in the second group, 10 is subtracted.
Moreover, some of us may have noticed that each of the larger added numbers is the result of the number preceding it multiplied by 5: 6 x 5 = 30 and 4 x 5 = 20.
Thus we have two means of arriving at the last number to be added:
20 – 10 = 10
2 x 5 = 10
We must now apply this rule to the last number shown in the series, i.e. we must add 10 to that number:
122 + 10 = 132.
The solution is therefore 132.
On the answer sheet, we must therefore mark the 1, the 2 and the 3.
