Missing Number
Missing number questions arrange numbers in rows (or a grid) that all follow the same arithmetic rule connecting the numbers in each row. The task is to find that rule from the complete rows, then apply it to the incomplete one.
Common patterns
- The third number is the product of the first two
- The third number is the sum of the first two
- A two-step rule, such as (a+b)×2
- A difference-of-squares relationship
Worked example
Question: 4,5,20 / 6,3,18 / 7,8,?
Answer: 56
Each row’s third number is the product of the first two: 7×8=56.
How to approach Missing Number
Identify the information given, test the simplest consistent rule, and verify that your rule explains every relevant part before answering.