Question

**Please help me** [WORK SHOWN]



Roberta deposited $3,116.92 into a savings account with an interest rate of 3.9% compounded quarterly. About how long will it take for the account to be worth $7,000?

14 years, 5 months

20 years, 10 months

21 years, 2 months

29 years, 11 months

With the equation I did I got 21 years, 2 months.
Am I correct?

3116.92(1+0.039/4)^4*21.2
= 7096.77

Answer 1

7000 = 3116.92(1 + 0.039/4)^4t = 3116.92(1.00975)^4t
7000/3116.92 = 2.24581 = 1.00975^4t
4tLog 1.00975 = Log 2.24581
4t ≈ 83.385
t = 20.846 ≈ 20 years 10 months

Answer 2

That's what popped up when I googled the answer

Answer 3

http://answers.yahoo.com/question/index?qid=20130203143656AARMtGE

Answer 4

yea why did you put that 21.2 in 3116.92(1+0.039/4)^4*21.2

Answer 5

Because that's how you do the formula

Answer 6

nope it isn't..you still don't get it?

Answer 7

Like for example, this question



Rachel deposited $6,449.82 into a savings account with an interest rate of 6.9% compounded annually. About how long will it take for the account to be worth $8,000?

3 years, 3 months

10 years, 10 months

12 years, 0 months

2 years, 4 months

Answer 8

6449.821+0.039/1)^1*3.3
= 8038.48

Answer 9

I used the same formula, the answer I chose was 3 years, 3 months and it was correct.

Answer 10

from where did that 3.3 pop up?

Answer 11

3 years, 3 months

Answer 12

means you are using guessed answer to calculate answer?

Answer 13

No? I'm using the formula given by my teacher to find the answer.

Answer 14

what if you didn't know 3.3 was the answer?

Answer 15

I did because I calculated EVERY single answer choice there, 3 years, 3 months WHICH COVERTED TO 3.3 was the only one over $8,000

Answer 16

you have to put t instead of 3.3 and then solve for t

Answer 17

10 years, 10 months = 10.10

12 years, 0 months = 12

2 years, 4 months =2.4

Answer 18

@stgreen has already told you the answer, but in general for most questions involving multiple choices, its better to find an equation and solve for the variable rather than plugging in the options as its far less time-consuming.

Answer 19

you calculated every single ans?that's laborious..you could've put t there and got the correct one in a single try

Answer 20

Well this was the formula given to me

Answer 21

@sumi29 explained my point

Answer 22

And I got the answer right using this formula

Answer 23

Oh well, whatever

Answer 24

@murrcat You can always get the right answer plugging in the options, but imagine for a moment, what happens if you pick two or three random choices out of four and all of them turn out to be wrong? You would have simply wasted your time, time that could've been well spent on constructing an equation and solving it for your answer. Your method is not wrong, its simply not worth the effort. I hope you get it.

Answer 25

Mhm