Ok, so i am collecting 50p pieces and arranging them on my desk in the shape of a triangle.

eg

50p

50p 50p

50p 50p 50p

50p 50p 50p 50p

I want to work out how much money I'm saving just by knowing how many rows of coins there are. If i can work out how many coins there are just by knowing how many rows I have I can just divide by 2 to find out the amount in dollars.