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Bunuel
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Bunuel
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ankushsambare
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Answer is C, and what makes this one click is realizing you never need to actually find the individual prices. The ratio is enough.

Let me set up the algebra. Let n, p, f = prices of notebook, pen, folder (same for both buyers).

The question asks: what fraction of Elena's total spending went to folders?
That's 10f / (6n + 9p + 10f).

Statement (1): Elena bought 6 notebooks, 9 pens, 10 folders.
Now we know Elena's quantities, but prices are still unknown. We can write her total as 6n + 9p + 10f, but we can't simplify the fraction without knowing the price ratios. Insufficient.

Statement (2): Riley bought 18 notebooks, 27 pens, 15 folders.
We know Riley's quantities, and we know Riley spent twice as much as Elena -- but we don't know Elena's purchase breakdown. Insufficient.

Combined:
Use the constraint: Riley's total = 2 x Elena's total.
18n + 27p + 15f = 2(6n + 9p + 10f)
18n + 27p + 15f = 12n + 18p + 20f
6n + 9p = 5f

Now substitute back into Elena's total:
6n + 9p + 10f = 5f + 10f = 15f

So the fraction on folders = 10f / 15f = 2/3.

The trap I fell for the first time I saw a problem like this: I spent 90 seconds trying to figure out whether the statements give us enough to solve for individual prices. They don't -- but that's not what you need. The "Riley spent twice as much" constraint links the two sets of quantities, which pins down the price relationship, which collapses the fraction.

This is a classic DS move: you don't need absolute values, just enough structure to fix a ratio.

Answer: C
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One can intuitively see that is Riley spends twice as Elena, then Riley should have had 20 folders, but she has only 15 folders.
Whereas we have 6N and 9P extra for Riley (when compared with 2x which is 9N and 18P)
Thus this 6N and 9P compensates for the loss in number of folders.
Or
6N+9P = 5F.
E-10F = 5F
E = 15F.
Bunuel
Elena and Riley each bought notebooks, pens, and folders from the same supplier. For each item type, the unit price was the same for Elena and Riley. If Riley’s total spending was twice Elena’s total spending, what fraction of Elena’s total spending was on folders?

(1) Elena bought 6 notebooks, 9 pens, and 10 folders.

(2) Riley bought 18 notebooks, 27 pens, and 15 folders.

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