Financial mathematics hp30b

[Danilton]

How to solve the following situation: During the first half of 2017, a certain commodity suffered the following price changes: in the first four months, successive and decreasing increases of 2%, where the first increase was 12%. In the next two months, it suffered successive and increasing discounts of 1%, where the first discount was 4%. At the end of the first half of 2017, this merchandise cost R $ 3,865,0095. What is the price of the merchandise at the beginning of 2017? (I'd like to put the amount of% per period / month in the calculator, but I only have the option to put a single value for all periods)

[Jan_D · Accepted solution]

Since all percentages differ I know no other way than to do it in 6 steps:

12%, 10%, 8%, 6%, 4%, 5%.

Of course you have to do it in reversed order so start with calculating back $ 3,865,0095 (?) with 5%.

Then calculating back the result with 4% and so on.

[Danilton]

I would like to put different percentages for each period in the calculator, it would be great

[Jan_D]

Have you tried to write a program?

I think it needs to be done in RPN mode, so it helps when you are familiar with that.

The program has to work as follows: you enter your value which you want to convert back, subsequently the interest rate, and your program has to calculate the previous value.

Once you have such a program you can enter your value,enter the interest rate, run the program, enter the next interest rate, run the program, enter the next interest rate, run the program and so on.

So this works very fast.

There are 2 ways to create the program:

First: when you know which (TVM) keystrokes in RPN mode you need to do this by hand you can enter this sequence into the program.

Second: There is an easy mathematical formula to calculate the conversion. Enter the keystrokes in RPN mode into the program.

[Danilton]

Okay, I'll try to program.

[Danilton]

I can not program, it's very complicated

[Jan_D]

What is the problem?

Can you create a simple program but not a more complicated program in RPN mode, or can not you write any program at all?

Do you understand the example on pages 77 and 78 of the User's Guide?

If not, what is the problem?

http://h10032.www1.hp.com/ctg/Manual/c02651527

[Danilton]

The problem is that I bought this calculator a short time, I still have not learned to program, its tip was very good, I will study the pages 77,78,79 and 80. thank you very much

[Danilton]

The program I want is similar to this example 2, take a look https://support.hp.com/br-pt/product/hp-30b-business-professional-calculator/4031708/model/4031709/d...

[Jan_D]

It is much simpler. We do not need loops.

We go back to the example in the first message:

12%, 10%, 8%, 6%, 4%, 5%.

Suppose the amount of money at the end of this period is 100.

We want to know what the amount is a month before.

The interest in this period is 5% per year.

We press: 100 FV, 5 I/YR, 1 N, 0 PMT, 12 Shift P/YR (shift is the blue bar at the lower left side of the calculator)

We now solve for PV by pressing PV and we get –99.58

I do not like the minus sign and press +/- to get rid of it.

So this is our answer.

Another way is to do it mathematically.

We call the amount at the end: B and the amount a month before: A

Then: B=(1+In/1200)*A, where In is the interest per year.

So A=B/(1+In/1200)

Now set your calculator to RPN mode.

Enter 100, the amount of money, press INPUT

Enter 5, the interest rate, press INPUT

Enter 1200, press division sign :

Enter 1, press +

Enter division sign :

Our result is now again 99.58, what it should be.

We can now write a program with content:

1200:1+:

Is not that a short program?

When you have made your program enter 100, press INPUT

Enter 5, press INPUT

Run the program

You will see 99.58

Now enter the next interest rate: 4, press INPUT

(I am not sure whether it is necessary to press INPUT in this case, you can test it)

Run the program and you will get your next answer.

Enter the next interest rate, which is 6, press INPUT

Run the program and so on.

I wonder if you get this working and know what you are doing!