How to calculate 1 share movement
The price of a share has two components: Bid: The highest price that someone who wants to buy shares is willing to pay for them. Ask: The lowest price that someone who has a share is willing to sell it for. The ask is always higher than the bid, since if they were equal the buyer and seller would have a deal, make a transaction, and that repeats until they are not equal. For stock with high volume, there is usually a very small difference between the bid and ask, but a stock with lower volume could have a major difference. When you say that the share price is $100, that could mean different things. You could be talking about the price that the shares sold for in the most recent transaction (and that might not even be between the current bid and ask), or you could be talking about any of the bid, the ask, or some value in between them. If you have shares that you are interested in selling, then the bid is what you could immediately sell a share for. If you sell a share for $100, that means someone was willing to pay you $100 for it. If after buying it, they still want to buy more for $100 each, or someone else does, then the bid is still $100, and you haven't changed the price. If no one else is willing to pay more than $90 for a share, then the price would drop to $90 next time a transaction takes place and thats what you would be able to immediately sell the next share for. Unless other people believe you have a reason for selling at a lower price, your sale probably has no lasting effect at all on the market. Of course, if people see you dump a few million dollars' worth of shares at a discount, they may be inclined to believe you have a reason. But if you just sell a few, they will conclude the reason is just that you needed cash in a hurry.
The point of that question is to test if the user can connect shares and stock price.  However, that being said yeah, you're right. Probably gives off the impression that it's a bit elementary. I'll look into changing it asap. Your observation is mostly right, that 1 is a the number around which this varies.  You are actually referencing PEG, P/E to Growth ratio, which is a common benchmark to use to evaluate a stock. The article I link to provides more discussion. "One of two things is true: You own less than 5% of the total shares outstanding. Your transaction will have little to no effect on the market. For most purposes you can use the current market price to value the position. You own more than 5% of the total shares outstanding. You are probably restricted on when, where, and why you can sell the shares because you are considered part owner of the company. Regardless, how to estimate (not really ""calculate,"" since some of the inputs to the formula are assumptions a.k.a. guesses) the value depends on exactly what you plan to with the result." "For the first and last questions, I can do this multiple ways.  For the middle question, I'll just make up values.  If you want different ones, you will have to redo the math.   I am going to assume that you participate in the merger exchange, swapping your share for their offer.   If you own one share, it depends how they handle fractional shares.  Your original one share of ABC can be worth either one share of XYZ or 1.05 shares of XYZ.  If you get one share, you typically get an additional $.80 cash to make up for the fractional share.   You might ask why you don't just get $20 cash and one share of XYZ.  Consider the case where you own twenty shares of ABC.  Then you'd own twenty-one shares of XYZ and $384.  No need for fractional shares.   Beyond all this though, the share value of XYZ is not set autocratically.  The shares might be worth $16, $40, or $2 after the merger.  If both stocks are perfectly valued and the market is aware of that value, then it will depend partially on the number of shares of each.   For example, if we assume there are 10,000 shares of ABC and 50,000 shares of XYZ (including the shares paid for ABC), then their initial market values are $320,000 for ABC and $800,000 for XYZ.  XYZ is paying $360,000, so its value drops to $440,000.  But it is gaining ABC, which is worth $320,000.  Net value now is $760,000 or $15.20 per share.   This has assumed that the shares transferred from XYZ to the shareholders of ABC were already included in the market value.  This may mean that the stock price was previously $20 or so with almost 40,000 shares in circulation.  Then they issued new shares, diluting the value down to $16.  We could start at 50,000 shares at $16 and end up with 60,000 to 60,050 shares at $13.332 to $13.333 per share.  Then XYZ is really only paying $326,658.31 for ABC.  That's a premium of only $6,658.31 for ABC and gives a final stock value of $13.222 per share.   The problem though is that in reality, there is no equivalent of perfect value.  So I say again that the market value might be $15.20 (the theoretic answer that best fits the question given the example quantities of shares), $13, $20, or something else.  It will depend on how the market perceives the deal.  Is the combined company worth more or less than the sum of its parts?   And beyond this, you will have $19.20 to $20 in cash in addition to your XYZ share (or 1.05 shares).  Assuming 1.05 shares, that would be $15.96 plus the $19.20--that's $35.16 total in theory or anything from $19.20 up in practice.  With the givens, the only thing of which you can be sure is the $19.20 cash.  The value of the stock is up in the air.   If XYZ is only privately traded, this is still true.  The stock is worth the price that someone will pay for it.  The ""someone"" is just more limited with privately traded stocks." "The best place to start looking is the companies ""Balance Sheet"" (B/S).  This would show you the total shares ""outstanding."" The quarterly B/S's arent audited but a good starting point.  To use in any quant method, You also need to look a growth the outstanding shares number. Company can issue shares to any employee without making a filing.  Also, YOU will NEVER know exactly the total number because of stock options that are issued to employees that are out of the money arent account for. Some companies account for these, some dont.  You should also explore the concepts of ""fully dilute"" shares and ""basis"" shares. These concepts will throw-off your calc if the company has convertible bonds." "According to the following article the answer is ""first-in, first-out"": http://smallbusiness.chron.com/calculate-cost-basis-stock-multiple-purchases-21588.html According to the following article the last answer was just one option an investor can choose: https://www.usaa.com/inet/pages/advice-investing-costbasis?akredirect=true" Let's suppose your friend gave your $100 and you invested all of it (plus your own money, $500) into one stock. Therefore, the total investment becomes $100 + $500 = $600. After few months, when you want to sell the stock or give back the money to your friend, check the percentage of profit/loss. So, let's assume you get 10% return on total investment of $600.  Now, you have two choices. Either you exit the stock entirely, OR you just sell his portion. If you want to exit, sell everything and go home with $600 + 10% of 600 = $660. Out of $660, give you friend his initial capital + 10% of initial capital. Therefore, your friend will get $100 + 10% of $100 = $110. If you choose the later, to sell his portion, then you'll need to work everything opposite. Take his initial capital and add 10% of initial capital to it; which is $100 + 10% of $100 = $110. Sell the stocks that would be worth equivalent to that money and that's it. Similarly, you can apply the same logic if you broke his $100 into parts. Do the maths. i will not calculate it for you but just calculate the discounted cash flow (by dividing with 1.1 / 1.1^2 / 1.1^3   ...)of each single exercise as stated and deduct the 12.000 of the above sum.  in the end compare which has the highest npv "Generally if you are using FIFO (first in, first out) accounting, you will need to match the transactions based on the number of shares. In your example, at the beginning of day 6, you had two lots of shares, 100 @ 50 and 10 @ 52.  On that day you sold 50 shares, and using FIFO, you sold 50 shares of the first lot.  This leaves you with 50 @ 50 and 10 @ 52, and a taxable capital gain on the 50 shares you sold. Note that commissions incurred buying the shares increase your basis, and commissions incurred selling the shares decrease your proceeds.  So if you spent $10 per trade, your basis on the 100 @ 50 lot was $5010, and the proceeds on your 50 @ 60 sale were $2990.  In this example you sold half of the lot, so your basis for the sale was half of $5010 or $2505, so your capital gain is $2990 - 2505 = $485. The sales you describe are also ""wash sales"", in that you sold stock and bought back an equivalent stock within 30 days.  Generally this is only relevant if one of the sales was at a loss but you will need to account for this in your code.  You can look up the definition of wash sale, it starts to get complex. If you are writing code to handle this in any generic situation you will also have to handle stock splits, spin-offs, mergers, etc. which change the number of shares you own and their cost basis.  I have implemented this myself and I have written about 25-30 custom routines, one for each kind of transaction that I've encountered.  The structure of these deals is limited only by the imagination of investment bankers so I think it is impossible to write a single generic algorithm that handles them all, instead I have a framework that I update each quarter as new transactions occur." There isn't a formula like that, there is only the greed of other market participants, and you can try to predict how greedy those participants will be. If someone decided to place a sell order of 100,000 shares at $5, then you can buy an additional 100,000 shares at $5. In reality, people can infer that they might be the only ones trying to sell 100,000 shares right then, and raise the price so that they make more money. They will raise their sell order to $5.01, $5.02 or as high as they want, until people stop trying to buy their shares. It is just a non-stop auction, just like on ebay. Elaborating on kelsham's answer: You buy 100 shares XYZ at $1, for a total cost of $100 plus commissions. You sell 100 shares XYZ at $2, for a total income of $200 minus commissions. Exclusive of commissions, your capital gain is $100 for this trade, and you will pay taxes on that.  Even if you proceed to buy 200 shares XYZ at $1, reinvesting all your income from the sale, you still owe taxes on that $100 gain.  The IRS has met this trick before. Try to find the P/E ratio of the Company and then Multiply it with last E.P.S, this calculation gives the Fundamental Value of the share, anything higher than this Value is not acceptable and Vice versa. 1 lot is 100 shares on London stock exchange Of course, this calculation does not take into consideration the fact that once the rights are issues, the price of the shares will drop. Usually this drop corresponds to the discount. Therefore, if a rights issue is done correctly share price before issuance-discount=share price after issuance. In this result, noone's wealth changes because shareholders can then sell their stock and get back anything they had to put in. You say: Every time it seems the share price dips. Does it?  Have you collected the data?   It may just be that you are remembering the events that seem most painful at the time. To move the market with your trade you need to be dealing in a large amount of shares.    Unless the stock is illiquid (e.g most VCT in the UK), I don’t think you are dealing in that large a number; if you were then you would likely have access to a real time feed of the order book and could see what was going on.