Question

You invest $4000 in a bank account with 5% interest compounded annually. You are wondering how long it would take for your money to double.

What equation will you use to solve the problem and how long will it take for your money to double?

Answer 1

40 yrs

Answer 2

14.2, 2, 7, or 28 years

Answer 3

the formula you want to use is:
\[A=A_o(1+\frac{r}{n})^{nt }\]
where A_o also called P is the initial amount (or principal amount)
r is the rate
n is the number of times the thing is compounded per year
t is the number of years you want to see how much money you have grown

Answer 4

so what is the initial amount \[A_o\]
?

Answer 5

hold on

Answer 6

dang it idk sorry.. i know i did it wrong

Answer 7

You invest $4000 in a bank account with 5% interest compounded annually. You are wondering how long it would take for your money to double.
read your question
it tells you what is the initial investment

Answer 8

i know but i just dont know how to work it out. i took the formula you gav me and put it in my caculator but i did it wrong

Answer 9

Can you tell me what the \[A_o\] is?

Answer 10

http://media.education2020.com/evresources/4072-06-01-04-00_files/i0270001.jpg

Answer 11

can you tell me what the initial investment is please!
this is \[A_o\] I have been talking about

Answer 12

8000 is certainly not the value you started with

Answer 13

how much did the guy invest?

Answer 14

i knwo im just guessing :(

Answer 15

i got 80

Answer 16

You invest $4000 in a bank account with 5% interest compounded annually. You are wondering how long it would take for your money to double.

This is your question.

I'm telling you to read the question. I'm not asking for any math yet.
I want you to tell me what you think is \[A_o\]
This \[A_o\]
represents the amount you started with.

Answer 17

4000 is the investment

Answer 18

How much money did you put in the bank account?

Answer 19

right so that is \[A_0\]
\[A=A_0(1+\frac{r}{n})^{nt}\]
so I'm going to replace A_0 with 4000 like so
\[A=4000(1+\frac{r}{n})^{nt}\]

Answer 20

thank you

Answer 21

writing this down* lol

Answer 22

You invest $4000 in a bank account with 5% interest compounded annually. You are wondering how long it would take for your money to double.

now I agree with your 1.05 for the inside
since r is .05 and n is 1
\[A=4000(1+\frac{.05}{1})^{1 \cdot t}\]

Answer 23

now how much do you expect to get at the end (also called A)?

Answer 24

once you give me that value I will put in the place of A in this equation:
\[A=4000(1.05)^t \]

Answer 25

i put this in my cacuator? 4000(1+.05/1)?

Answer 26

nope you can't that one part has an unknown exponent
I'm asking you for a value
still not asking for any math
I want you to tell me what we expect to get in the end
read your question

Answer 27

5%

Answer 28

I thought 5% was the rate (and it is)

Answer 29

ohh i ahve no clue how to find the value..:(

Answer 30

You invest $4000 in a bank account with 5% interest compounded annually. You are wondering how long it would take for your money to double.

4000 was the initial
.05 was the rate
n was 1 (because it was compounded once a year)
t is the unknown because it says how long
A is the amount I'm asking for right now
A symbolizes what we will get in t years

Answer 31

I need you to read your question and take a deep breath because your question does tell tell you how much you would end up with in t years.

Answer 32

Was does the second sentence say?

Answer 33

all i know is that is says about it being doubled

Answer 34

is that it? i keep reading it and i already gave you the other numbers

Answer 35

so if the initial is 4000
and we want to end up with double that what does that mean?

Answer 36

add it

Answer 37

what is double 4000?

Answer 38

add it

Answer 39

what is 2(4000)?

Answer 40

oh mutliply !

Answer 41

well you could say 4000+4000

Answer 42

8000

Answer 43

it equals 8000

Answer 44

ok so 8000 is the amount we want to end with it after t years

Answer 45

so that goes in place of A

Answer 46

\[8000=4000(1.05)^t \]
now you need to solve this equation for t

Answer 47

i add 400 and 1.05 right?

Answer 48

nope

Answer 49

i dont know how to solve equations either i forgot..

Answer 50

srry

Answer 51

you need to isolate the thing that has the unknown first
(1.05)^t is being multiplied by 4000
how do you undo multiplication by 4000?

Answer 52

you divide

Answer 53

right so divide both sides by...?

Answer 54

4000?

Answer 55

ok

Answer 56

and 800?

Answer 57

where does 800 come from?

Answer 58

whatever you do to one side of the equation you do to the other side

Answer 59

if you divide 4000 on one side you must do it to the other side
tell me what you get when you divide 4000 on both sides

Answer 60

okay so i divide 4000 and 4000 that cancels so 4000/1.05 and that equals 3809.5

Answer 61

I'm not sure how you got that

Answer 62

im gonna go craqzy... i suck retriceat this

Answer 63

you told me you were going to divide both sides by 4000
what happened to doing just that?