Texas Instruments PLUS TI-89 - Manual (Page 422)

Chapter 23: Activities 405
23ACTS.DOC TI-89/TI-92 Plus: Activities (English) Susan Gullord Revised: 02/23/01 1:24 PM Printed: 02/23/01 2:20 PM Page 405 of 26
In the Program Editor, define the following Time-Value-of-Money
(
tvm ) function where temp1 = number of payments, temp2 = annual
interest rate, temp3 = present value, temp4 = monthly payment,
temp5 = future value, and temp6 = begin- or end-of-payment period
(1 = begining of month, 0 = end of month).
:tvm(temp1,temp2,temp3,temp4,temp5,temp6)
:Func
:Local tempi,tempfunc,tempstr1
:
ë temp3+(1+temp2/1200 ù temp6) ù temp4 щ ((1 м (1+temp2/1200)^
( ë temp1))/(temp2/1200)) ì temp5 ù (1+temp2/1200)^( ë temp1)
! tempfunc
:For tempi,1,5,1
:"temp"&exact(string(tempi))
! tempstr1
:If when(#tempstr1=0,false,false,true) Then
:If tempi=2
:Return approx(nsolve(tempfunc=0,#tempstr1) | #tempstr1>0 and
#tempstr1<100)
:Return approx(nsolve(tempfunc=0,#tempstr1))
:EndIf
:EndFor
:Return "parameter error"
:EndFunc
Find the monthly payment on 10,000 if you make 48 payments at 10%
interest per year.
On the Home screen, enter the tvm
values to find pmt .
Result: The monthly payment is
251.53.
Find the number of payments it will take to pay off the loan if you
could make a 300 payment each month.
On the Home screen, enter the tvm
values to find n .
Result: The number of payments
is 38.8308.
Computing the Time-Value-of-Money
This activity creates a function that can be used to find the
cost of financing an item. Detailed information about the steps
used in this example can be found in Chapter 17: Programming.
Time-Value-of-
Money Function
Tip: You can use your
computer keyboard to type
lengthy text and then use
TI-GRAPH LINK to send it
to the TI - 89 / TI - 92 Plus.
Finding the Monthly
Payment
Finding the Number
of Payments