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: 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.