There are 10 checkpoints in a 4500 orienteering course.

Checkpoint 1 is the start and the checkpoint 10 is the finish. The distance between successive checkpoints increases by 50 meters as each checkpoint is passed.
The distance, in meters between checkpoint 2 and checkpoint 3 is?

Question

There are 10 checkpoints in a 4500 orienteering course. 

Checkpoint 1 is the start and the checkpoint 10 is the finish. The distance between successive checkpoints increases by 50 meters as each checkpoint is passed. 
The distance, in meters between checkpoint 2 and checkpoint 3 is?

dehelloo · Answer

It's arithmetic sum. 

So I'd solve for a 

4500=9/2(2a + (9-1) 50= But that equals  275 as the starting value

And once I find the sum of the second cone 600 and sum of 3rd cone 975 and subtract I get 375. 

But thats wrong as on the Multiple Choice theres only

a) 225
B) 275
C) 300
D)350
E) 400