2007 AMC 12A Problems/Problem 7
Problem
Let a, b, c, d, and e be five consecutive terms in an arithmetic sequence, and suppose that a+b+c+d+e=30. Which of a, b, c, d, or e can be found?
Solution
- a=c-2f
- b=c-f
- c=c
- d=c+f
- e=c+2f
- a+b+c+d+e=5c=30
- c=6
- But we can't find any more variables, because we don't know what f is.
