This is a fairly straightforward problem where you have to combine two ratios to obtain a new ratio. If you have practiced sufficient problems on this concept, this question is actually an easy question.

Ratio of Vodka to orange juice = 2:3; ratio of orange juice to tonic water = 2:1.
To combine the two ratios, multiply the first ratio by 2 and the second ratio by 3. On doing this, we get,
Ratio of Vodka to orange juice to tonic water = 4:6:3.

Let us assume that there are 4 ounces of Vodka, 6 ounces of orange juice and 3 ounces of tonic water.
Now, if 3 more ounces of tonic water are added to the drink, we will have 6 ounces of tonic water. This makes the ratio of orange juice to tonic water 1:1. But the proportions cannot be changed, as per the question. So, we need to add 6 more ounces of orange juice to maintain the original ratio of 2:1.

Using a similar analogy, it is not difficult to understand that, for 12 ounces of orange juice (remember you added 6 more to the original 6), there needs to be 8 ounces of vodka to maintain the ratio of 2:3. But we only had 4 ounces originally; this means we have to add 4 more ounces to maintain the final ratio of 4:6:3.

After all the additions, let’s see what we have:
4 + 4 = 8 ounces of Vodka
6 + 6 = 12 ounces of orange juice
3 + 3 = 6 ounces of tonic water.
The numbers 8, 12 and 6 are definitely in the ratio of 4:6:3. This is a very simple way of verifying the answer that we got.

So, the correct answer option is C.

A couple of things to note about ratio questions. One – always take simple values to mirror the ratio given, instead of taking variables. Two – always verify your answers by checking if it satisfies the ratio provided. Also remember that ratio questions are best suited to be solved using answer options, so, employing methods like elimination and back solving will save time and energy.

Hope this helps!
Arvind,
CrackVerbal PrepTeam
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We have v : o as 2 : 3 and o : t as 2 : 1. We must reconfigure these two ratios to make them compatible. The way to do this is to “match” the numbers for orange juice with the common multiple of 6. Thus, the first ratio will now be v : o is 4 : 6, and the second ratio will now be o : t is 6 : 3. The 3-way ratio can now be expressed as v : o : t is 4 : 6 : 3.

Vodka : OJ: Tonic Water = 4x : 6x : 3x

If we let x = 1, then we currently have 4 ounces, 6 ounces and 3 ounces of vodka, OJ, and tonic water, respectively, in the drink.

If 3 ounces of tonic water is added, then we would have 6 ounces of tonic water, and we would need to have 12 ounces of OJ and 8 ounces of vodka. So we need 4 more ounces of vodka.

Answer: C
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Thank you for the detailed solution, much appreciated.
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these questions about drinks makes me eager to take a break and have some fun after I do well on the GMAT!

Thanks for the inspiration!

Vodka : OJ = 2 : 3 = 4 : 6
OJ : Tonic water = 2 : 1 = 6 : 3

So Vodka : OJ : Tonic water = 4 : 6: 3

So 3 ounces of tonic water needs 4 ounces of vodka.
Answer (C)
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Solution: Vodka (V): Orange (R) = 2: 3 = 4: 6
And Orange (R): Tonic Water (W) = 2: 1 = 6:3
Now, V: R: W = 4: 6: 3

If 3 ounces of tonic water are added to the drink, then the amount of tonic water will be 6.
The resulting solution will be: V: R: W = 4*2: 6*2: 3*2 = 8:12: 6
Therefore, additional 4 ounces of Vodka must be added.
Answer: C