Consider the set S = {1, 2, 3, ..., 1000}. How many arithmetic progressions can be formed
Consider the set S = {1, 2, 3, ..., 1000}. How many arithmetic progressions can be formed from the elements of S that start with 1 and end with 1000 and have at least 3 elements?
- 3
- 4
- 6
- 7
Answer
Let the number of elements in a progression be n, then
1000 = 1 + (n-1)d
(n-1)d = 999 = 27 * 37
Possible values = 3, 37, 9, 111, 27, 333, 999
The correct option is D.