## sara1234 2 years ago Tired doing several times and keep getting weird answer?

1. sara1234

can any one show me steps how to do this so i can see where i went wrong i keep getting 0.6918

2. yummydum

2835.48= 2310.72(1+r/2)^10 1.2271 = (1+r/2)^10 1.02067 = 1+ r/2 .02067 = r/2 r = 0.04135 => 4.1%

3. yummydum

@jim_thompson5910

4. jim_thompson5910

Roberta deposited \$4,790.23 into a savings account with an interest rate of 3.8% compounded twice a year. About how long will it take for the account to be worth \$9,000? A = P(1+r/n)^(nt) 9000 = 4790.23(1+0.038/2)^(2t) solve for t

5. sara1234

but i don't understand the logitude part? the in idk how to do it

6. sara1234

i'll do what i can and stop where i don't undersstand okay hold on

7. jim_thompson5910

alright

8. sara1234

9000 = 4790.23(1+0.038/2)^(2t) 9000=4790.23(1+0.038/2)^2t ----- -------- 1.8788=1.019^2t 1.8788=1.0383t t=1.8094??

9. jim_thompson5910

no it's much more than 1.8 years

10. sara1234

i know next i have to do a proportion that idk how to do

11. jim_thompson5910

A=P(1+r/n)^(n*t) 9000=4790.23(1+0.038/2)^(2*t) 9000=4790.23(1+0.019)^(2*t) 9000=4790.23(1.019)^(2*t) 9000/4790.23 = (1.019)^(2*t) (1.019)^(2*t) = 9000/4790.23 (1.019)^(2*t) = 1.87882 log( (1.019)^(2*t) ) = log( 1.87882 ) 2t*log( 1.019 ) = log( 1.87882 ) 2t = log( 1.87882 )/log( 1.019 ) 2t = 33.506118 t = 33.506118/2 t = 16.753059 t = 16.75 t = 16+0.75 years t = 16 years + 0.75 years t = 16 years + 0.75*12 months t = 16 years + 9 months t = 16 years, 9 months

12. jim_thompson5910

The key to solving for t, which is in the exponent, is to use logs to isolate it

13. jim_thompson5910

A=P(1+r/n)^(n*t) A=7775(1+0.045/n)^(n*14) Now plug in n = 365. If you get 14,398.87 for A, or close enough to it, then the answer is "daily". If not, then move onto n = 12, n = 4, and n = 1 until you find your answer.

14. sara1234

for 365 i got 12960.26204

15. jim_thompson5910

you should have gotten A = 14597.86 when n = 365

16. jim_thompson5910

try it again I recommend using a graphing calculator and using the table if you can

17. sara1234

ohh i got it its 14597.85537

18. sara1234

so its daily

19. jim_thompson5910

yep, it's daily

20. sara1234

oh i get it 365=daily 12=monthly 1-yearly quartly=4 right?

21. jim_thompson5910

yep n = 365 means you compound 365 days a year (assuming not a leap year)

22. jim_thompson5910

ie you compound 365 times a year

23. jim_thompson5910

n = 4 means you compound 4 times a year, etc etc

24. sara1234

it wasn't daily check what went wrong