sigma notation??

Question

sigma notation??

anonymous · Answer

attachment

tkhunny · Answer

20(0.5^2 + 0.5^3 + ... + .05^11)

It's a finite geometric series.  Can you add it up?

anonymous · Answer

Ahhh definitely! Thanks!

anonymous · Answer

I got 7.5?

anonymous · Answer

Pretty sure I'm not right, lol.

hero · Answer

But 7.5 isn't even one of the answer choices is it?

anonymous · Answer

No...

anonymous · Answer

I got .375 when I added everything, then times it by 20

hero · Answer

When I calculate it, I get one of the answer choices.

anonymous · Answer

OHHH wait, I forgot to do 5^11 i added it just as 5 okay wait I'm gonna try again

anonymous · Answer

wait no, I actually did add it by 5^11 the first time...

hero · Answer

What did you input into your calculator when you computed the sum?

anonymous · Answer

0.5^2 + 0.5^3 +  .05^11 then I times that by 20

anonymous · Answer

Do I have to foil it? Sorry I don't get it

hero · Answer

Basically, any time you see the three dots between terms, it means the sum continues:

20(0.5^2 + 0.5^3 + ... + .05^11) = 
                                                      20(0.5^2 + 0.5^3 + 0.5^4 + 0.5^5 + 0.5^6 
                                                      + 0.5^7 +  0.5^8 + 0.5^9 + 0.5^10 + 0.5^11)

hero · Answer

I hope you are able to make sense of that

anonymous · Answer

I think so, thank you

anonymous · Answer

I got it! 9.99

hero · Answer

Correct