400. Is there a mathematical formula to determine a stock's price at a given time?
I found the answer. It was the Stock Ticker that I was looking for. So, if I understand correctly the price at certain moment is the price of the latest sale and can be used to get a global picture of what certain stock is worth at that certain instant.

401. Is 0% credit card utilization worse than 1-20% credit card utilization for any reason other than pure statistics?
The whole point of a credit report and, by extension, a credit score, is to demonstrate (and judge) your ability to repay borrowed funds.  Everything stems from that goal; available credit, payment history, collections, etc all serve to demonstrate whether or not you personally are a good investment for lenders to pursue. Revolving credit balances are tricky because they are more complicated than fixed loans (for the rest of this answer, I'll just talk about credit cards, though it also applies to lines of credit such as overdraft protection for checking accounts, HELOCs, and other such products). Having a large available balance relative to your income means that at any time you could suddenly drown yourself in debt.  Having no credit cards means you don't have experience managing them (and personal finances are governed largely by behavior, meaning experience is invaluable).  Having credit cards but carrying a high balance means you know how to borrow money, but not pay it back.  Having credit cards but carrying no balance means you don't know how to borrow money (or you don't trust yourself to pay it back). Ideally, lenders will see a pattern of you borrowing a portion of the available credit, and then paying it down.  Generally that means utilizing up to 30% of your available credit.  Even if you maintain the balance in that range without paying it off completely, it at least shows that you have restraint, and are able to stop spending at a limit you personally set, rather than the limit the bank sets for you. So, to answer your question, 0% balance on your credit cards is bad because you might as well not have them.  Use it, pay it off, rinse and repeat, and it will demonstrate your ability to exercise self control as well as your ability to repay your debts.

402. How can I get the car refinanced under my name if my girlfriend signed for the loan?
The best solution is to "buy" the car and get your own loan (like @ChrisInEdmonton answered). That being said, my credit union let me add my spouse to a title while I still had a loan for a title filing fee.   You may ask the bank that holds the title if they have a provision for adding someone to the title without changing the loan.   Total cost to me was an afternoon at the bank and something like $20 or $40 (it's been a while).

403. Why do some online stores not ask for the 3-digit code on the back of my credit card?
@Jeremy Using CVV doesn't decrease the transaction cost. I know this because I have quotes for CC transactions and the cost/transaction doesn't depend on using CVV. That said we don't plan to use CVV because we sell insurance and the likelihood that someone who steals CC will buy insurance is very low.

404. Where can I find the nominal price of a stock prior a split into multiple companies?
Yahoo Finance provides the proper closing price.  HP's historical data around the split date can be found here. The open, high and low of the day are wrong prior the split, but the closing price is right and for HP, it was $26.96 USD.  The next day the closing price was $13.83 USD.

405. Can PayPal transfer money automatically from my bank account if I link it in PayPal?
I linked my bank account (by making a transfer from bank account to Paypal) without linking a card. This should not give Paypal any rights to do anything with my bank account - transfer that I made to link it was exactly the same as any other outgoing transfer from my bank account. On attempting to pay more that resides in my Paypal balance I get  To pay for this purchase right now, link a debit or credit card to your PayPal account. message. Paypal is not mentioning it but one may also transfer money to Paypal account form bank to solve this problem. Note, that one may give allow Paypal to access bank account - maybe linking a card will allow this? Paypal encourages linking card but without any description of consequences so I never checked this. It is also possible that Paypal gained access to your bank balance in other way - for example in Poland it just asked for logins and passwords to bank accounts (yes, using "Add money instantly using Trustly" in Poland really requires sharing full login credentials to bank account - what among other things breaks typical bank contract) source for "Paypal attempts phishing": https://niebezpiecznik.pl/post/uwaga-uzytkownicy-paypala-nie-korzystajcie-z-najnowszej-funkcji-tego-serwisu/

406. How does Value Averaging work in practice?
Value averaging has you shift the balance of your portfolio over time, not the amount of contributions.  So you can only do it if you have a portfolio holding both risky assets (shares etc) and some cash. You start out by making a plan about how much you will contribute every month and at what rate you expect the share part of the portfolio to grow.  Perhaps based on 20th century data you think an 8% growth rate is reasonable.  Or alternatively if you know your desired final amount obviously you can work backwards to a desired rate from that. If in any month the share part is falling below its expected growth path, you would put more money into it: possibly your whole paycheck contribution plus some from the savings cash account.  On the other hand if the share component is growing "too fast" you would put all your additional savings into cash.  So if your investments are doing well, you're not supposed to spend the excess money, but rather to put it aside into a dedicated cash account to top up your share component when prices fall. In theory, this has the auto-levelling benefit of Dollar Cost Averaging, but even better: when prices are high, you'll automatically buy fewer shares, or even sell some; conversely when prices are low you'll buy extra shares from your reserve account. If it turns out your estimate was unreasonably optimistic, and over your lifetime shares only ever average 3%, you'll end up with an entirely share portfolio, and a bumpier ride than you might have liked.  If you have horrible luck and over your entire investing life shares return less than cash (which has happened, though not yet in the USA), then this will be worse than a standard balanced portfolio. The original book Value Averaging by Edelson has a pretty good explanation of various cases, though I would say some of the examples are worked in excessive detail. I have not implemented this myself, one reason being that the amount I'm able to save from year to year varies, as it probably does for you, and so predicting a path is not quite so simple as he assumes.  You could still do it I suppose. I think you could get a very crude approximation to this by simply directing your savings into cash when the share market's rate of growth over the last several years is above what you think is the long term average.

407. If I put a large down payment (over 50%) towards a car loan, can I reduce my interest rate and is it smart to even put that much down?
Talk to your bank first but shop around a bit as well with other reputable lenders in your area.  Another option, if you're willing to put down ~84% of the purchase price would be to talk to several dealerships BEFORE you set foot on a single lot. Tell them that you are interested in buying a Versa and that you are willing to pay cash but you are not willing to pay more than $10,200. They won't agree (trust me on that) but they will come down from $13,000. Say "Thanks, I'll call you back." and call one of the other dealerships on your list and tell them "I just spoke with this dealership and they are willing to sell me the car for [whatever number they gave you]." One of two things will happen, either the dealership will come back with a lower price or they will tell you to go buy the car there. Continue this process until you have one dealership left.  I did this with 3 dealerships in 2011 and bought a truck with a $27,000 sticker price for just over $19,000. It took about a week to make all of the calls and I ended up going to a dealership 3 hours away but it was worth it for $8,000.

408. What is the difference between trading and non-trading stock?
Every company has Stocks.   For the stocks to be traded via some stock exchange, the companies must follow the eligibility criteria and guidelines. Once done, these are then listed on the stock exchange and can be traded. The advantage [amongst others] of listing is liquidity and stocks can easily be bought and sold.  Some small companies or closely held companies may not want to list on stock exchange and hence are not traded. This does not mean they can't be bought and sold, they can be outside of the market, however the deals are complex and every deal has to be worked out. During the course of time a stock that is traded on a stock exchange, would either fail to meet the criteria or voluntarily choose not to be traded and follow the delisting process [either by stock exchange or by company]. After this the stocks are no longer traded on the exchange.

409. New to Stock Trading
Good ones, no there are not.  Go to a bookstore and pick up a copy of "The Intelligent Investor."  It was last published in 1972 and is still in print and will teach you everything you need to know.  If you have accounting skills, pick up a copy of "Security Analysis" by Benjamin Graham.  The 1943 version was just released again with a 2008 copyright and there is a 1987 version primarily edited by Cottle (I think).  The 1943 book is better if you are comfortable with accounting and the 1987 version is better if you are not comfortable and feel you need more direction. I know recent would seem better, but the fact that there was a heavy demand in 2008 to reprint a 1943 book tells you how good it is.  I think it is in its 13th printing since 2008.  The same is true for the 72 and 87 book.  Please don't use internet tutorials.  If you do want to use Internet tutorials, then please just write me a check now for all your money.  It will save me effort from having to take it from you penny by penny because you followed bad advice and lost money.  Someone has to capture other people's mistakes.  Please go out and make money instead.   Prudence is the mother of all virtues.

410. Pros and Cons of Interest Only Loans
Given the current low interest rates - let's assume 4% - this might be a viable option for a lot of people.  Let's also assume that your actual interest rate after figuring in tax considerations ends up at around 3%.  I think I am being pretty fair with the numbers. Now every dollar that you save each month based on the savings and invest with a higher net return of greater than 3% will in fact be "free money".  You are basically betting on your ability to invest over the 3%.  Even if using a conservative historical rate of return on the market you should net far better than 3%.  This money would be significant after 10 years.   Let's say you earn an average of 8% on your money over the 10 years.  Well you would have an extra $77K by doing interest only if you were paying on average of $500 a month towards interest on a conventional loan.  That is a pretty average house in the US.  Who doesn't want $77K (more than you would have compared to just principal).  So after 10 years you have the same amount in principal plus $77k given that you take all of the saved money and invest it at the constraints above. I would suggest that people take interest only if they are willing to diligently put away the money as they had a conventional loan.  Another scenario would be a wealthier home owner (that may be able to pay off house at any time) to reap the tax breaks and cheap money to invest. Pros: Cons: Sidenote:  If people ask how viable is this.  Well I have done this for 8 years.  I have earned an extra 110K.  I have smaller than $500 I put away each month since my house is about 30% owned but have earned almost 14% on average over the last 8 years.  My money gets put into an e-trade account automatically each month from there I funnel it into different funds (diversified by sector and region).  I literally spend a few minutes a month on this and I truly act like the money isn't there.  What is also nice is that the bank will account for about half of this as being a liquid asset when I have to renegotiate another loan.

411. Credit card transactions for personal finances
I use mint.com for tracking my finances.  It works on mobile phones, tablets, and in a browser.  If you don't mind the initial hassle of putting in the credentials you use to access your account online, you'll find that you're able to build a comprehensive picture of the state of your finances relatively quickly. It does a great job of separating the various types of financial transactions you engage in, and also lets you customize those classifications with tags.  It's ad-supported, so there's no out-of-pocket cost to you, and it doesn't preclude you from using the personal finance software you already have on your phone.

412. Can a bank statement be submitted as a proof of investment?
Probably not. A debit of 50K in your Bank statement does not mean that its invested into tax saving instrument. This question is best answered by the finance department of your company. Practise vary from organization to organization.

413. Stock Exchange in US
The easiest route for you to go down will be to consult wikipedia, which will provide a comprehensive list of all US stock exchanges (there are plenty more than the ones you list!). Then visit the websites for those that are of interest to you, where you will find a list of holiday dates along with the trading schedule for specific products and the settlement dates where relevant. In answer to the other part of your question, yes, a stock can trade on multiple exchanges. Typically (unless you instruct otherwise), your broker will route your order to the exchange where it can be matched at the most favorable price to you at that time.

414. How will Brexit affect house mortgages?
Only you can decide whether it's wise or not given your own personal circumstances. Brexit is certainly a big risk, and noone can really know what will happen yet. The specific worries you mention are certainly valid. Additionally you might find it hard to keep your job or get a new one if the economy turns bad, and in an extreme "no deal" scenario you might find yourself forced to leave - though I think that's very unlikely. House prices could also collapse leaving you in "negative equity". If you're planning on staying in the same location in the UK for a long time, a house tends to be a worthwhile investment, particularly as you always need somewhere to live, so owning it is a "hedge" against prices rising. Even if prices do fall, you do still have somewhere to live. If you're planning on going back to your home country at some point, that reduces the value of owning a house. If you want to reduce your risk, consider getting a mortgage with a long-term fixed rate. There are some available for 10 years, which I'd hope would be enough to get us over most of the Brexit volatility.

415. Can I claim a tax deduction for working from home as an employee? I work there 90% of the time
The short answer is yes you probably can take the deduction for a home office because the space is used exclusively and you are working there for the convenience of your employer if you don't have a desk at your employers office. The long answer is that it may not be worth it to take the home office deduction as an employee. You're deduction is subject to a 2% AGI floor. You can only deduct a percentage of your rent or the depreciation on your home. A quick and dirty example if you make $75k/year, rent a 1200 sqft 2 bedroom apartment for $1000/month and use one bedroom (120 sqft) regularly and exclusively for your employer. You can deduct 10% (120sqft/1200sqft) of the $12000 ($1000*12 months (assumes your situation didn't change)) in rent or $1200. However because you are an employee you are subject to the 2% AGI floor so you can deduct $1200-$1500 (75000*.02 (salary * 2% floor)) = -300 so in order to deduct the first dollar you need an additional $300 worth of deductible expenses.  Depending on your situation it may or may not be worth it to take the home office deduction even if you qualify for it.

416. How to prevent myself from buying things I don't want
Nathan's answer was a +1 from me. The answer is not always simple. Having the money available is surely the first step. Using Pete's process aligns with this.  Another thought is depending where you are in your finances, delay by a day for every $100 in cost. e.g. For a $1000 purchase, sleep on it for 10 days. Adjust the number for your circumstance.
