Math help

Okay I am having trobule with my math assignment, here is the question:
4. a)Using the method in 3, write the average number of dots in each row for a triangular arry with n dots on each side.
I got this covered the formula is (n+1)/2
b)Multiply the rows in expression 4. a) by the number of rows to obtain an expression for the number of dots in an triangular array.
There is a image with this, i will show you, *'s representing dots:
*
**
***
****
*****
V
V
********
*********

WTN(What the duece)? Got no clue what you're talking about, but your teacher must be mad in giving you homework when you could be posting. Try explaining you're problem better, I didn't quite understand it.

Sorry, here is the page, dont mind my notes
This is page two i need help on 4 b,c and 5
http://tinypic.com/52deh3
I uploaded page 1.

i think that formula is wrong. though i'm not sure what it would be.

anyway, what you're trying to do is find the number of total dots in any given N,
to do this we need to treat it as a triangle. and find the area.

A = (BH)/2

but your not exactly doing a basic triangle... it's a triangle + a little bit.
our base and hight are equal, they equal that of N,
so:

A = (NN)/2 = (N^2)/2

take N being 5, like you have.
5 dots down X 5 dots across = 25 dots.
25 dots/2 = 12.5

but because here we divided exactly in half, we need to add half of N

so 12.5 + N/2 = 15.

so your formula is N^2/2 + N/2 (for question b)
or you could do nC3, if you know how...

and in question a.. since your taking the average, you would divide the total by N.

so question a = (N^2/2+N/2)/N

i hope you understood all that, cause it would help you.

edit: after looking at your pic... you're right, (n+1)/2 works. i can't believe i forgot that. i feel like a moron.
(but that stuff up there still works.)