finding annuity: Billy wants to retire in 30 years....

korean

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I hope I put this subject in the right area...If not admins please repost this in the right forum & please and let me know by private message or email. thanks

well here are my two problems. (word problems)

1.) Billly wants to retire in 30 years. He has a balance of $12,000 in his 401(k) plan. Billy expects to need about $865,000 to meet all his needs for retirement living. He expects his investments to earn about 10% annualy (meaning 10% per year) for the next 30 years. calculate the amount he needs to save annually for the next 30 years to accumulate $865,000.

next.

2.) Jane in the same situation as Billy except that she has two children and she feels that she cannot really save more than $1,000 annually towards retirement for the next 10 years. She, however, also feels that she can save substantially more after 10 years. Calculate the amount she would need to save annually after year 10 in order to achieve her retirement goal.


my answers that i tried to do by myself is this (PLEASE LET ME KNOW IF IM WRONG OR I NEED CORRECTIONS!!!)

FIRST THE EQUATIONS THAT IM AM USING ARE.....(PLEASE LET ME KNOW IF IM USING THE WRONG EQUATIONS OR IF THEY NEED TO BE ADJUSTED OR IF I NEED ANOTHER EQUATION THAT I DONT HAVE!!!)

fv - future value fva - future value of annuity
pv - present value pva - present value of annuity
I - interest
N- total number of periods
A - annuity/payments

EQ1.) fv = pv(1+I)^N
EQ2.) fva = A * {[(1+I)^N - 1] / I}
EQ3.) pv = fv / (1+I)^N
EQ4.) pva = A * {[1 - (1 / (1+I)^N)] / I}

Answer 1.) pv = $12,000 and fv = $865,000
so i find what $12,000 would be in 30 years with 10% interest by doing

12000(1.10)^10 = 209392.82 (EQ1)

then i subtract the two numbers.
865000-209392.82 = 655607.18 so this is the amount i have for the fv after accounting for the 12000

so then i use EQ2 to find the annuity for each year.

655607.18 = A * {[(1.10)^10 - 1] / .10]
655607.18 = A * (164.4940227)
A = 3985.60

so for the first one i get $3985.60

Answer 2.) pretty much the same stuff but im getting messed up on the $1000 stuff and accounting for that and other complications here is what i did so far.

i got to the point like the first answer for accounting for the 12000 so my fv is 655607.18 but how do i account for the $1,000 for 10 years and the 20 years after the previous 10? And how do i find the annuity amount after years 10? im so lost on this one? please help!!
 
so sorry... i did figure i might or might not use this as well.... but how and why to use it...beats me

fva = 1000 * {[(1.10)^10 - 1] / .10} = 15937.4244 ~ $15937.42
 
korean said:
so sorry... i did figure i might or might not use this as well.... but how and why to use it...beats me
fva = 1000 * {[(1.10)^10 - 1] / .10} = 15937.4244 ~ $15937.42

That's correct; now you need the fv of that for 20 years: 15937.42(1.10^20)

Subtract result from the 655607.18 that's left after accounting for the 12000.

Now find the required annual amount, over 20 years (not 30); OK?
 
Re: finding annuity

korean said:
so for the first one i get $3985.60
That's what I get, too. Good work.

If Jane were retiring in 10 years, how much would she have?

12000*(1.1)^10 = 31,124.90 <== Rounded

1000*[(1+i)^10 - 1]/i = 15,937.42 <== Rounded

That's a total of 47,062.32

Now solve the previous problem, but starting with 47,062.32 and saving for only 20 years.

There are other ways.
 
ok thanks i think i got it but can you let me know if im on the right track or not here is what i did for the answer 2.

with the 12000 i found the fv and it is 209392.82 so i subtract that amount from 865000 which gives me 655607.18... from the above answer in 1.

then i find the fva of the 1000 which came to be 15937.42
then i take that and find the rest of the interest for the next 20 years and that came out to be 107219.05...from there i subtract that amount from the 655607.18 to get a an amount that is 548388.13.

this would be (i think) my fv minus the fv of the 12000 and fva of the 1000. please correct me if im am wrong!

from then on i take the 548388.13 as my fva and solve for the remaining 20 that i have missed and this is how i came to that conclusion and answer.


fva = A * {[(1+I)^N - 1] / I} so..

548388.13 = A * {[(1.10)^20 - 1] / .10}
548388.13 = A * (57.27499949)
A = 9574.65.............so would this by my answer?? or do i go further or am i just plain wrong at it....i tried to understand what you guys told me and tried to apply it as the best as i can but i think i might be wrong...can you guys please check my answer and let me know???

thanks
korean. :D
 
korean said:
ok thanks i think i got it but can you let me know if im on the right track or not here is what i did for the answer 2.

with the 12000 i found the fv and it is 209392.82 so i subtract that amount from 865000 which gives me 655607.18... from the above answer in 1.

then i find the fva of the 1000 which came to be 15937.42
then i take that and find the rest of the interest for the next 20 years and that came out to be 107219.05...from there i subtract that amount from the 655607.18 to get a an amount that is 548388.13.

this would be (i think) my fv minus the fv of the 12000 and fva of the 1000. please correct me if im am wrong!

from then on i take the 548388.13 as my fva and solve for the remaining 20 that i have missed and this is how i came to that conclusion and answer.


fva = A * {[(1+I)^N - 1] / I} so..

548388.13 = A * {[(1.10)^20 - 1] / .10}
548388.13 = A * (57.27499949)
A = 9574.65.............so would this by my answer?? or do i go further or am i just plain wrong at it....i tried to understand what you guys told me and tried to apply it as the best as i can but i think i might be wrong...can you guys please check my answer and let me know???

thanks
korean. :D
I agree with your handling of the fv of the $1000 payments and confirmed your calculations using a spreadsheet. Good work!
 
Good work, k :wink:

Making up something like this "to guide you on your way" can be useful:

0: 12000
1: 1000
...
10: 1000 : x
11: y
...
30: y : 865000
 
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