Finding a Missing Number in a Sequence
Counting numbers have an order. You may need to find a number that is missing from a group of numbers. The numbers may be counting up or counting down.
See if the other numbers are counting up or counting down.
Find the missing number that completes the count up or count down.
Finding a Missing Number in a Sequence
How to find a missing number in a sequence
Determine if the order of numbers is ascending (getting larger in value) or descending (becoming smaller in value).
Find the difference between numbers that are next to each other.
Use the difference between numbers to find the missing number.
Example: Find the missing number: 15, 13, ?, 9
The order of numbers is going down or descending.
The difference between numbers is 15  13 = 2
Since the order is descending subtract 2 from 13. The missing number may be 11.
The missing number is 11 since it is 2 more than the last number 9.
Activity: Find the Missing Number.

