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 - 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: 18, 15, ?, 9 - The order of numbers is going
down or descending. - The difference between numbers is 18 - 15
= 3 - Since the order is descending subtract 3 from 15. The
missing number may be 12. - The missing number is 12 since it is
3 more than the last number 9.