What is the average of the first 30 positive integers?

Hi all, I'm guessing 15 but

How do you figure this problem out, that is:

what is the layout of the math reasoning?

(I'm trying to learn more about number properties/interrelations etc)

Studying for an exam for Monday... your help is appreciated

thanks

Here's another prob:

A is 1,000(1+2+ ...+100)

B is 2,000(1+2+ ...+100)

B-A would be 1,000(1+2+ ...+100) , right?

Then how can you know without doing the summing, what

1,000(1+2+ ...+100) is?

Is there a "trick" to the number relationships?

One thing, we know that 100+99 is 199 almost 200 so 1,000*200 is 200,000 so the answer would have to be more than that.

is this the only way to "figure " this out? or are there other ways?

ok