fozzzy wrote:

Sorry bad phrasing, suppose there are 2 quantities and we assign variables to them. The total amount of money spent is 1000 and one person spends more than the other. How do we decide if person A is 1000- X or person B is X.

an example would be question 71 from

OG 13 - 2 categories.

Yesterday's closing prices of 2,420 different stocks... initial words of that question

You assign the variable x to one person, say person A spends x. The other one is fixed then. Then B must spend 1000 - x. When you make your desired equation, you will get the value of x. Now you know that person A spends x and B spends 1000 - x. If A spends more, automatically x will be greater than 1000 - x.

You can also go the other way around - B spends x while A spends 1000 - x. Your equation will change now and values of x will change too. Now x will be less than 1000 - x. B spends x and A spends 1000 - x.

The final answer will be the same in both the cases.

or if you talk about the question in OG, you can assign x to stocks that went down and make the equation as

(120/100)x + x = 2420

x = 1100 = stocks that went down

2420 - x = 1320 = stocks that went up

or

you can assign x to stocks that went up and make the equation as

x + (100/120)x = 2420 (x is 20% more than the stocks that went down so x = (120/100)*stocks that went down )

x = 1320 = stocks that went up

2420 - x = 1100 = stocks that went down

Notice that values of x in the two cases are different (since x stands for different things) but overall the answer is the same.

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