Let us discuss what to look for in solving a number series question
Examine the difference between adjacent numbers.
→ In a simple series, the difference between two consecutive numbers is constant.
Logic: There is a difference of (99) between each item. The missing number in this case is 431.
→ In a more complex series the differences between numbers may be dynamic rather than fixed, but there still is a clear logical rule.
Example: 3, 4, 6, 9, 13, 18, __
Logic: Add 1 to the difference between two adjacent items. After the first
number add 1, after the second number add 2 and after the third number
add 3, etc. In this case, the missing number is 24.
2. See whether there is a multiplication or division pattern between two adjacent numbers.
Example: 64, 32, 16, 8, __
Logic: Divide each number by 2 to get the next number in the series.
The missing number is 4.
3. Check whether adjacent numbers in the series change based on a logical pattern.
Example: 2, 4, 12, 48, __
Logic: Multiply the first number by 2, the second number by 3 and the third number by 4, etc. The missing item is 240.
4. See if you can find a rule that involves using two or more basic arithmetic functions (+, -, ÷, x). In the below series, the functions alternate in an orderly fashion.
Example: 5, 7, 14, 16, 32, 34, __
Logic: Add 2, multiply by 2, add 2, multiply by 2, etc. The missing item is 68.
Tip: Series’ in this category are easy to identify. Just look at the numbers that do not appear to have a set pattern.
In a series that involves two or more basic arithmetic functions, the differences between adjacent items effectively create their own series. We recommend that you try to identify each pattern separately.
Example: 4, 6, 2, 8, 3, __
Logic: In this series, the differences themselves create a series: +2, ÷3, x4, -5
The numbers advance by intervals of 1 and the arithmetic functions change in an orderly sequence. The next arithmetic function in the series should be +6, and so the next item in the series is 9 (3+6 = 9).