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

**The solution is A] 40**as all the numbers in the given series are even.

**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

**Solution – D] 17**. Notice the series corresponds to consecutive prime numbers with 17 being the next prime number

Q) 5 10 17 26 ?

A] 15

B] 10

C] 11

D] 17

E] 37

Solution

**Solution – E] 37**.

The series is related to the square of numbers as following :

5 = 2^{2}+1

10 = 3^{2}+1

17 = 4^{2}+1

26 = 5^{2}+1

Hence the next number is 37 = 6^{2}+1

Q) 343 119 49 70 ?

A] 763

B] 62

C] 52

D] 111

E] 57

Solution

**Solution – A] 763**. Notice that all the numbers are divisible by 7.

Q) 3 11 85 1029 ?

A] 14590

B] 62456

C] 15631

D] 1564

E] 599

Solution

**Solution – C] 15631**

Notice the series is of the form

3 = 1^{2}+2

11 = 2^{3}+3

85 = 3^{4}+4

1029 = 4^{5}+5

Hence, the next number is 15631 (5^{6}+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