Sigma Notation HELP!!!

Question

anonymous · Answer

$$\sum_{n=1}^{12}2n+5$$
a. 29
b. 36
c. 216
d. 432

anonymous · Answer

$$\sum_{n=2}^{10}-2n-3$$
a. −270
b. −135
c. 135
d. 270

anonymous · Answer

Let's look at this.
The sigma is telling us that n =1, n=2, n=3 . . . n=12

2(1) + 5, 2(2) + 5) . . . 2(12) + 5

Are you with me so far?

anonymous · Answer

$$\sum_{n=3}^{12}20(0.5)^{n-1}$$
a. 9.99
b. 19.95
c. 29.98
d. 39.96

anonymous · Answer

$$\sum_{n=1}^{5}3(-2)^{n-1}$$
a. −93
b. −33
c. 33
d. 93

anonymous · Answer

If you could also explain how to do it so I can do it on my own in the future that would be great. The lesson did a poor job of explaining it so I don't understand it at all. Thanks. 
Medal for best answer.

anonymous · Answer

@kirbylegs No, I don't:/ Sorry, I don't get sigma notations at all. Like, what do the numbers on top and bottom mean?