According to the directions on a can of frozen orange juice concentrate, 1 can of concentrate is to be mixed with 3 cans of water to make an orange juice. How many 12 ounce cans of concentrate are required to prepare 200 6-ounce servings of orange juice?
It's almost always the case that GMAT tutoring students miss that this is just a ratio. You're making a solution (the orange juice) that has a certain mix of different ingredients (water and concentrate) that are in a certain proportion. That screams: ratio! For GMAT ratio questions I like making a ratio box to organize the information. You don't always have to use it but often the ratio box is a helpful tool. On the top of the box you've got your Ratio, Multiplier, and Real. You multiply the ratio by the multiplier to get to the real world values. The multiplier is always the same all the way down. Notice that you can sum your Ratio column to the get the ratio total. Same for the Real. You can't sum the multiplier column.
Now that we've got our information in the ratio box hopefully we can make some inferences. In total we've got 1200 ounces of orange juice. For that 1200 ounces we need 300 ounces of concentrate. The cans have 12 ounces of concentrate. So 300/12 = 25. Done. Comment with any questions or additions!