Math Help

Grimsin · 01-24-12, 11:23 AM

I have a number, its a money value, I need to subtract 20% from it. how would you do that? then display the new number? since i cant use %'s

Xrystal · 01-24-12, 11:31 AM

20% is the same as 0.20 so multiply by 0.x for any percentage to get the percentage amount then deduct it from the original amount.

There is another way to get the result straight off but the above is the simplest method.

Dridzt · 01-24-12, 11:52 AM

money*0.8

All the money functions return copper amount.

So just use amount * 0.8 (that's 80%) then format it to gold silver copper with one of the built-in functions.

(can look it up, don't remember it off-hand)

Xrystal · 01-24-12, 12:30 PM

ah thats it ... result = ( money * ( 1 - (percent/100) )

if percent is 20 then this would come out as

(money * ( 1 - (20/100))
(money * ( 1 - 0.2))
(money * 0.8)

It would then work for any percentage you need.

Grimsin · 01-24-12, 12:51 PM

This produced proper results -

Code:

GameTooltip:AddDoubleLine("Friendly Discount", addon:MoneyToString(floor(totalCost * 0.95), true))
	GameTooltip:AddDoubleLine("Honored Discount", addon:MoneyToString(floor(totalCost * 0.9), true))
	GameTooltip:AddDoubleLine("Revered Discount", addon:MoneyToString(floor(totalCost * 0.85), true))
	GameTooltip:AddDoubleLine("Exaulted Discount", addon:MoneyToString(floor(totalCost * 0.8), true))

Phanx · 01-25-12, 12:40 AM

Originally Posted by Xrystal

20% is the same as 0.20 so multiply by 0.x for any percentage to get the percentage amount then deduct it from the original amount.

What kind of schools are people attending where they don't learn about percents?

zork · 01-25-12, 03:20 AM

One of the best things when it comes to percentages is the "Dreisatz" (rule of proportion).

http://en.wikipedia.org/wiki/Rule_of_proportion

So easy example. You have 100$. That is 100% of your money. You want so substract 20% of it. So you can write down:

Code:

100$     x
----  =  ---
100%     80%

x is the value you want to calculate and it is 100%-20% = 80% of your money.

Now all you have to do is to make the value for x come out. (Having x stand on one side)

To make that possible you multiplay both side of the equation with 80%. By doing that the 80% on the right side will fade because 80% / 80% is 1.

Code:

100$*80%      x*80%
--------   =  ---
100%          80%

100$*80%      x*1
--------   =  ---
100%          1

100$*80%      
--------   =  x
100%

Result:

Code:

x = 100$*80%/100%

x = 80$

The cool thing about that is that even the suffixes come out accordingly. The % delete themselve only the $ stays. Btw. 8000/100 is the same as 100*0.8. Doesn't matter.

**Seerah** · 01-25-12, 01:44 PM

I have never, ever seen that method using proportions before, Zork.

(At least in America) we teach that this is how to use proportions to solve percent problems.

Code:

 percent     portion 
--------- = ---------
   100        whole

so, let's say you want 80% of 200:

Code:

 80       x  
----- = -----
 100     200

Then you cross-multiply

Code:

80 * 200 = 100 * x

divide by 100 on both sides to solve for x

Code:

( 80 * 200 ) / 100 = 100x / 100
160 = x

(I'm a math teacher.)

Ither · 01-25-12, 03:54 PM

Originally Posted by Seerah

I have never, ever seen that method using proportions before, Zork.

No disrespect, but that's because you're American?

Dreisatz is taught at realschulen (secondary school) in many European countries. I learned it and I live in Germany, well did until I moved to America.

Xrystal · 01-25-12, 05:52 PM

It's been a long while since I did basic maths in school in the UK but Seerah's way did look a lot more familar than Zorks. But then again things can change in 30 years rofl.

The way I mentioned was from my time as an accountancy software programmer. We had to use formulae like that all the time to get tax and discount calculations right.