# Simple mathematical formula. Help **URL:** \ **Category:** Factual Questions\ **Tags:** science-math\ **Created:** [February 15, 2024, 1:17am UTC](https://boards.straightdope.com/t/simple-mathematical-formula-help/997585 "2024-02-15T01:17:18Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![peedin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/peedin/32/14095_2.png) [@peedin](https://boards.straightdope.com/u/peedin)\ **Post date:** [February 15, 2024, 1:17am UTC](https://boards.straightdope.com/t/simple-mathematical-formula-help/997585/1 "2024-02-15T01:17:19Z")
I don’t remember grammar school math. Here is the problem. Please show your work so I can remember. I need to withdraw money and net $15K. I need to withdraw enough to cover 20% of that $15k in taxes. How much do I need to withdraw? Is it 20% of $15k = $3k so I need $18k? ---
**Author:** ![Snarky\_Kong](https://avatars.discourse-cdn.com/v4/letter/s/a183cd/32.png) [@Snarky\_Kong](https://boards.straightdope.com/u/Snarky_Kong)\ **Post date:** [February 15, 2024, 1:23am UTC](https://boards.straightdope.com/t/simple-mathematical-formula-help/997585/2 "2024-02-15T01:23:05Z")
0.8 \* withdrawn = $15,000 withdrawn = 15k / 0.8 withdrawn = 18,750 Assuming you messed up “I need to withdraw enough to cover 20% of $15k.” Because yes, that’s just calculating 20% of 15k. ---
**Author:** ![OldGuy](https://avatars.discourse-cdn.com/v4/letter/o/3bc359/32.png) [@OldGuy](https://boards.straightdope.com/u/OldGuy)\ **Post date:** [February 15, 2024, 1:38am UTC](https://boards.straightdope.com/t/simple-mathematical-formula-help/997585/3 "2024-02-15T01:38:03Z")
If you literally mean you need to cover 20% of the $15K in taxes, you’re right. But I suspect you mean you need to cover 20% of the amount withdrawn. In that case then Snaky\_Kong is right. ---
**Author:** ![peedin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/peedin/32/14095_2.png) [@peedin](https://boards.straightdope.com/u/peedin)\ **Post date:** [February 15, 2024, 1:48am UTC](https://boards.straightdope.com/t/simple-mathematical-formula-help/997585/4 "2024-02-15T01:48:09Z")
It’s bad that I cannot explain what I need! Snarky\_Kong is right. The feds are going to take 20% of whatever I draw, so how much do I need to take out to net $15k? ---
**Author:** ![PastTense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pasttense/32/14550_2.png) [@PastTense](https://boards.straightdope.com/u/PastTense)\ **Post date:** [February 15, 2024, 2:09am UTC](https://boards.straightdope.com/t/simple-mathematical-formula-help/997585/5 "2024-02-15T02:09:32Z")
Snarky\_Kong gave you the answer: You withdraw $18,750. The government takes 20% of that which is $3,750 which leave you with $15,000. ---
**Author:** ![peedin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/peedin/32/14095_2.png) [@peedin](https://boards.straightdope.com/u/peedin)\ **Post date:** [February 15, 2024, 5:07am UTC](https://boards.straightdope.com/t/simple-mathematical-formula-help/997585/6 "2024-02-15T05:07:38Z")
I was restating the question, which Snarky\_Kong answered. Now I have the formula. ---
**Author:** ![InternetLegend](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/internetlegend/32/13154_2.png) [@InternetLegend](https://boards.straightdope.com/u/InternetLegend)\ **Post date:** [February 15, 2024, 5:54am UTC](https://boards.straightdope.com/t/simple-mathematical-formula-help/997585/7 "2024-02-15T05:54:23Z")
I just want to say that it does my heart good to see that I’m not the only one who is occasionally stopped cold by the inability to come up with a simple math formula. We should have remedial math classes for adults who’ve been out of the classroom too long! ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [February 15, 2024, 6:08am UTC](https://boards.straightdope.com/t/simple-mathematical-formula-help/997585/8 "2024-02-15T06:08:34Z")
In the spirit of “show your work”, it may or may not be helpful here to work through the algebra a bit more completely. You need to withdraw x, where x - 0.2x = 15,000 so, working through and solving for x: x (1 - 0.2) = 15,000 0.8x = 15,000 x = 18,750 ---
**Author:** ![Thudlow\_Boink](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/thudlow_boink/32/320_2.png) [@Thudlow\_Boink](https://boards.straightdope.com/u/Thudlow_Boink)\ **Post date:** [February 15, 2024, 12:23pm UTC](https://boards.straightdope.com/t/simple-mathematical-formula-help/997585/9 "2024-02-15T12:23:22Z")
Problems involving percents aren’t really difficult, but they are tricky and easy to get wrong, because you have to pay attention to what you’re taking a percentage **of**. ---
**Author:** ![Pardel-Lux](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pardel-lux/32/20182_2.png) [@Pardel-Lux](https://boards.straightdope.com/u/Pardel-Lux)\ **Post date:** [February 15, 2024, 12:41pm UTC](https://boards.straightdope.com/t/simple-mathematical-formula-help/997585/10 "2024-02-15T12:41:34Z")
Problems involving percentages are also tricky because they are not reversible. If you start with 100 and add 50% you get 150. If you then take 50% away again you end up with only 75, not 100. But if you do it the other way around, first substracting and then adding, you get the same result. ---
**Author:** ![Mighty\_Mouse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mighty_mouse/32/7776_2.png) [@Mighty\_Mouse](https://boards.straightdope.com/u/Mighty_Mouse)\ **Post date:** [February 15, 2024, 12:45pm UTC](https://boards.straightdope.com/t/simple-mathematical-formula-help/997585/11 "2024-02-15T12:45:44Z")
I cannot count the number of Vice Presidents and Director of Finance I have had the misfortune of working with who cannot convert the following statement to a percentage increase: “We had Sales of $15.0 million which was $3 million higher than the previous year” Most of the time they will get 20%, when it should be 25%. I have seen this mistake literally hundreds of times by people earning more than a quarter million a year presumably in part due to their financial acumen. ---
**Author:** ![Thudlow\_Boink](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/thudlow_boink/32/320_2.png) [@Thudlow\_Boink](https://boards.straightdope.com/u/Thudlow_Boink)\ **Post date:** [February 15, 2024, 12:46pm UTC](https://boards.straightdope.com/t/simple-mathematical-formula-help/997585/12 "2024-02-15T12:46:12Z")
> [@Pardel-Lux](#): > > Problems involving percentages are also tricky because they are not reversible. If you start with 100 and add 50% you get 150. If you then take 50% away again you end up with only 75, not 100. Right, and that’s exactly because you’re taking percents of different numbers each time. One example I like to use is: Suppose your boss says to you: “I’m going to have to give you a 50% pay cut, but to make it up to you I’ll immediately follow it up with a 60% raise. Is that okay with you?” ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [February 15, 2024, 1:50pm UTC](https://boards.straightdope.com/t/simple-mathematical-formula-help/997585/13 "2024-02-15T13:50:19Z")
On the off chance there’s more behind the question the OP asked … You’d only need to pay taxes on a withdrawal if the money is coming from a traditional (= not Roth) IRA or 401K. And if the withdrawal is not being moved into a different IRA or 401K. Even then, you do not _need_ to send the IRS their cut at the same time. You _can_ choose to wait and pay them next April15th in 2025 when you file your 2024 income taxes. Or you could pay them any time between now and then. You might owe a smidgen of interest if you waited another 14 months to pay, but depending on what the money is invested in, you _might_ do better leaving the money for taxes inside the account between now and then. ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [February 15, 2024, 2:25pm UTC](https://boards.straightdope.com/t/simple-mathematical-formula-help/997585/14 "2024-02-15T14:25:06Z")
> [@Mighty\_Mouse](#): > > “We had Sales of $15.0 million which was $3 million higher than the previous year” > > Most of the time they will get 20%, when it should be 25%. > > I have seen this mistake literally hundreds of times by people earning more than a quarter million a year presumably in part due to their financial acumen. There’s really no excuse for this kind of mistake, but one can see the origin of it, and it’s a little like those mathematical word games phrased as trick questions. The problem is that people tend to focus on the numbers that are explicitly presented rather than bothering to comprehend the words. Or IOW, a key number here, “[sales in] the previous year” is presented as a non-numeric descriptor so there’s a tendency to gloss right by it. Although you’d certainly think that a finance person who is supposed to be good with numbers would know better! ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [February 16, 2024, 12:25am UTC](https://boards.straightdope.com/t/simple-mathematical-formula-help/997585/15 "2024-02-16T00:25:42Z")
> [@Thudlow\_Boink](#): > > Suppose your boss says to you: “I’m going to have to give you a 50% pay cut, but to make it up to you I’ll immediately follow it up with a 60% raise. Is that okay with you?” Related to this, most financial modeling starts with an assumption of lognormal returns, rather than normal.