As the name suggests, in common rule series, all numbers follow a common mathematical rule.
Let’s start with an example:
Q) 2 4 8 16 20 ?
A] 40
B] 43
C] 45
D] 47
E] 41
Solution
TIP : Just when do we use the common rule technique to find the solution, given there may be many ways to decipher the series? The general idea is that when other techniques such as difference patterns don’t work out, that’s a great time to think about common rules binding the numbers together. Thus, the common rule method is a actually secondary method but is something IPAT takers must keep in their back pocket
Let’s go through a few more practice examples. Please do attempt the questions before reading the solutions 🙂
Q) 2 3 5 7 11 13 ?
A] 15
B] 10
C] 11
D] 17
E] 23
Solution
Q) 5 10 17 26 ?
A] 15
B] 10
C] 11
D] 17
E] 37
Solution
The series is related to the square of numbers as following :
5 = 22+1
10 = 32+1
17 = 42+1
26 = 52+1
Hence the next number is 37 = 62+1
Q) 343 119 49 70 ?
A] 763
B] 62
C] 52
D] 111
E] 57
Solution
Q) 3 11 85 1029 ?
A] 14590
B] 62456
C] 15631
D] 1564
E] 599
Solution
Notice the series is of the form
3 = 12+2
11 = 23+3
85 = 34+4
1029 = 45+5
Hence, the next number is 15631 (56+6)
Excellent job if you got the last question right!
Practice does help immensely, especially in the timed situation of the real test. We have developed a comprehensive numeric series question practice book specifically catering to the IPAT which you can find here