Like, if the Dow Jones went up by 100 points, the S & P went down 200 points, NASDAQ went up 100 points… how much in dollars would a $100,000 investment gain/lose?
Assuming that the $100,000 is spread across the three major indices and the smaller ones.
The easiest way to approach this problem: look at the percentage gain or loss of an index and apply that same percentage to an investment. A specific example: SPY is an index based on the S P 500. You can follow its daily fluctations alonside the index. You should note that they pretty much have a one to one correlation.