# Thread: I hate the calculator!

1. ## I hate the calculator!

I would like to be able to calculate compound interest using a calculator as follows:

enter lump sum
enter x
enter interest rate
enter =====

For example, if the lump sum is \$100 and the interest rate is (a whopping!) 8%, I would do the following:

Code:
`100 x 1.08 = = = = =`
And then I will get the compounded sum after 5 years of compounding.

I can do this with the calculator in windows, but not with one I have found in GNU/Linux.

Can you recommend a calculator that can do this?

Thank you!

2. A Carafe of Ubuntu
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Jul 2012
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## Re: I hate the calculator!

I have installed many calculators so I've forgotten what the default calculator is in Ubuntu. Have you tried gcalc? There is also xcalc. If you don't mind installing some additional components, there is also kcalc.

All of these are available in the software center. I'm not sure about xcalc ... you might have to do sudo apt-get install xcalc.
Last edited by ub07; July 25th, 2012 at 08:59 PM.

3. ## Re: I hate the calculator!

Try this. It does the same as you're doing but using maths not tricks.

C * (1 + r/100)^n

where C is the cash you start with, r the interest rate as a percentage, n the number of years to compound.

4. ## Re: I hate the calculator!

I don't know if this helps but you can use python

use

Code:
`python`
then type what your looking for
Code:
```2+2
2*2
2/2```
Code:
```rob@rob-mobile:~\$ python
Python 2.7.3 (default, Apr 20 2012, 22:44:07)
[GCC 4.6.3] on linux2
>>> 2*2
4
>>> 2+2
4
>>> 2/2
1
>>>```

5. 5 Cups of Ubuntu
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Jul 2012
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## Re: I hate the calculator!

He's right... the default calculator in Ubuntu doesn't support pressing "=" multiple times to repeat a function. I've never noticed this before, because I use the calculator for, er, mostly adding two numbers together

Pressing "=" more than once toggles between the answer you got, and the sum you entered (presumably so you can edit it and recalculate?).

Looking at what I have installed in Software Centre, the default calculator app ("Calculator") seems to be something called "gcalctool". It sounds like it's definitely got loads of features ("financial, logical and scientific modes") but the lack of support for re-pressing "=" seems like a funny omission.

Googling around, gcalctool is a default bit of Gnome, so I would even suggest that the OP raises it with the devs. Click here. It may be that there's a very good reason why they've gone with the "toggle" idea, but it's worth investigating.

6. Tea Glorious Tea!
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## Re: I hate the calculator!

Originally Posted by ub07
I have installed many calculators so I've forgotten what the default calculator is in Ubuntu. Have you tried gcalc? There is also xcalc. If you don't mind installing some additional components, there is also kcalc.

All of these are available in the software center. I'm not sure about xcalc ... you might have to do sudo apt-get install xcalc.
The default calculator in Ubuntu is gcalctool.

7. Eschew gratuitous obfuscation
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## Re: I hate the calculator!

Compound interest is easy. You're half way there by expressing the interest rate as 1.08. If you want to find out the effect of that over say 10 years you'd simply multiply by 1.08^10. If it was over 20 years it would be 1.08^20.

So yes, any calculator that does powers can do compound interest.

You can also use Libre Office Calc to do interest rates, it has pretty much the same functions available as MS Office.

8. 5 Cups of Ubuntu
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## Re: I hate the calculator!

Originally Posted by peter d
Try this. It does the same as you're doing but using maths not tricks.

C * (1 + r/100)^n

where C is the cash you start with, r the interest rate as a percentage, n the number of years to compound.
Peter D, you just blew my mind.

I'm terrible at maths. Brief off-topic - I used to work in a bar with an old guy who'd once known a minor mathematical celeb (I forgot the details, but he was a professor of maths who'd had a slot on some light TV game show, probably before I was born). In the pub, the prof was also a keen darts player.

For some reason, he could do all kinds of complex equations, but had a real blind spot for doing mental subtractions. Darts scores are all about subtractions. Apparently he kept getting it wrong and had to be corrected all the time.

Off-topic finished

9. 5 Cups of Ubuntu
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## Re: I hate the calculator!

On a more serious note, there are a lot of good suggestions here for rephrasing the requirement as a single equation... but a lot of calculator users won't be that good at maths. Isn't hitting "=" to repeat the operation a standard (useful) feature? It's a while since I've held a pocket calculator, but they all did it when I was young. There's a "lowest common denominator" aspect here.

For instance, it's easy to square a number (even I can do that) but the default calculator still has a button to do it for you.

Having said which - I am squirrelling these equations away for future reference

10. ## Re: I hate the calculator!

you can use gcalc's Fv function to calculate compounding interest, however, it uses a recurring payment method, assuming you are adding equal payments in at each period

for instance if I enter the following into the Fv function:
Periodic Payment: 100
Periodic Interest Rate: .08
Number of Periods: 5
I end up with 586.660096 as my answer

I'm not sure of an easy way to figure out a one-time payment compounding rate