unicornilove wrote:
Hi
MartyMurray, would you be able to take a stab at this?
Frankly I find the answers quite lacking and require an amount of prior understanding to understand which I do not have.... Also, is there a formula/method to address such questions?
I find it quite hard to accept that a constant removal and addition can be equated to a proportional reduction at every step..
Let's think about what's going on in this scenario.
Each time the process occurs, 8 liters of liquid is removed and replaced with 8 liters that contains no wine.
Of course, in each case, 8 liters is going to represent the same fraction of the liquid that's in the cask.
For example, if the amount of liquid in the cask is 32 liters, 8 liters will be \(\frac{1}{4}\) of the liquid each time.
So, let's see what happens if we remove the same fraction of liquid from the cask multiple times.
Let's say that the number of liters in the cask is \(x\).
We remove 8 liters of wine.
So, when we remove 8 liters of wine, the fraction of the total wine that we have removed is \(\frac{8}{x}\).
Then, the number of liters of wine left in the cask is \(x - 8\).
The fraction of original wine that will be left will be \(\frac{x - 8}{x}\).
Then, we replace what we have removed with water, and there's still \(x - 8\) liters of wine in the cask, along with 8 ilters of water.
Simple enough.
Now, you might think that the next time, we'd remove a different fraction of the wine because, the next time we remove 8 liters of liquid, there's less wine in the cask. However, notice the following.
When we remove 8 liters, we're still removing \(\frac{8}{x}\) of the liquid in the cask, which presumably is a homogenous mix of wine and water.
So, when we remove 8 liters, we remove \(\frac{8}{x}\) of the wine and \(\frac{8}{x}\) of the water.
So, with each removal and replacement,
we remove the same fraction of the remaining wine, which is \(\frac{8}{x}\), and replace it with water.
Now, the fraction of the wine that remains when we take out \(\frac{8}{x}\) of the wine is \(\frac{x - 8}{x}\) of the wine. So, after the process occurs 1 time, we have \(\frac{x - 8}{x}\) of the original amount.
After the process occurs 2 times, we have \((\frac{x - 8}{x})^2\) of the wine left.
After the process occurs 3 times, we have \((\frac{x - 8}{x})^3\) of the wine left.
After the process occurs 3 times, we have \((\frac{x - 8}{x})^4\) of the wine left.
Thus, since the ratio of wine to water is 16:65, and thus the ratio of wine to total is \(\frac{16}{16 + 65}\) = \(\frac{16}{81}\), \((\frac{x - 8}{x})^4 = \frac{16}{81}\).
Thus, \(\frac{x - 8}{x} =\) the fourth root of \(\frac{16}{81} = \frac{2}{3}\).
\(\frac{x - 8}{x} = \frac{2}{3}\)
\(3(x - 8) = 2x\)
\(3x - 24 = 2x\)
\(x = 24\)
Correct answer: B