## anonymous one year ago Evaluate S5 for 600 + 300 + 150 + … and select the correct answer below.

1. anonymous

2. anonymous

@surjithayer

3. anonymous

it should be greater than 1050 600+300+150+75+37.5=?

4. anonymous

I suppose so? Isn't it a geometric series?

5. anonymous

correct.

6. anonymous

So, would I be correct?

7. anonymous

hold on.

8. anonymous

600{(1/2)^5-1}/(1/2-1)

9. anonymous

@phi

10. anonymous

116.5 Am I right?

11. zepdrix

You're adding up 5 numbers. The first of which is 600. How did they then add up to 116.5? :o That's even smaller than the first number that you're adding... You silly billy -_-

12. anonymous

:D! Hahaha whoops! So what should I do?

13. zepdrix

$\large\rm S_n=a_1\frac{1-r^n}{1-r}$So you determined that your common ratio, $$\large\rm r$$, is 1/2 since you're dividing by 2 each time. So we'll plug in all of the information, $\large\rm S_5=600\cdot \frac{1-\left(\frac{1}{2}\right)^5}{1-\frac{1}{2}}$

14. zepdrix

And then let mr calculator do the rest :O understand how to punch it all in?

15. anonymous

Not really, but I'll try :)

16. anonymous

So, for the fraction part I got 1.9375.

17. zepdrix

If you want to punch it all in at once, I would try something like this,$\large\rm 600*((1-.5\wedge5)\div(1-.5))$Otherwise, if you like to do it piece by piece, that's fine also :)

18. zepdrix

(I replaced 1/2 with .5 in my calculator so it's easier to deal with).

19. anonymous

Ok:) Then, i got 1162.5 as an answer :)

20. zepdrix

1.9375? That sounds correct for your fractional part. Then finally 1162.5? Yayyy good job!

21. anonymous

Yippee!!! If, I post another one will you answer it? And thanks so much btw!!!

22. zepdrix

I'm hungrehhh, I need to make some foods :P but ya I'll try to come look if I get a chance. You can use the @zepdrix and it'll get my attention better than the message box.

23. anonymous

Ok, thanks so much:)