Question

Sum of a Geometric Series

Hey, can I please have some help with this question.

Evaluate:
18 + 9 + 4 1/2 + ... + 9/64

So A = 18
R = 2
How do I find "N"?

Answer 1

N = the number of terms ..

Answer 2

a1 = 18
r = 2
your ration is 1/2

Answer 3

ratio of terms

Answer 4

18/2 = 9
9/2 = 4 1/2

Answer 5

Yeah, I got it to 18x2^n-1 = 9/64

Answer 6

Then I went 2^n-1 = 81/32 but I do not know where to go from there

Answer 7

I do not know how to get it to same base

Answer 8

take the log

Answer 9

I do not know how to do that, we have not done logs yet

Answer 10

Just realised I had ratio of 2 instead of 1/2

Hopefully I can work it out now

Answer 11

Nope still have not got it

Answer 12

just keep dividing the ratios till you 9/64..
a1 = 18
a2 = 9
a3 = 4.5
a4 = 2.25
a 5 = 1.125
a6 = .5625
a7 = .28125
a8 = 0.140625
and there you have your answer n = 8
9/64 = 0 .140625

Answer 13

So no easier way? Just have to keep dividing?

Answer 14

there's an easier way... if you read what I gave you

Answer 15

well there probably is. i'm just too tired to find what it is.

Answer 16

Fair enough Shamil

And nin this type of question was not there

Answer 17

Dinner :P back in a bit

Answer 18

omg... you want to be spoon-fed

Answer 19

Yeah because I can not understand the question so i need explaining

Answer 20

Any help?

Answer 21

Don't worry, I had times 18 instead of divided 18

Thanks for the help