Bunuel
Tough and Tricky questions: Word Problems.
Three completely unmarked containers are used for measuring water. Water may be poured from one container to another, but no water may be poured outside the containers. Using nothing but the three containers and an unlimited supply of water, is it possible to measure exactly 4 gallons of water?
(1) The capacity of the first container is 2 gallons more than the capacity of the second container.
(2) The capacity of the second container is 2 gallons more than the capacity of the third container.
Kudos for a correct solution.If this were a usual puzzle, each statement alone would be sufficient but this is a data sufficiency question and you cannot assume anything so here the answer will be (C). Here is why:
Three containers and unlimited water. How will you measure 4 gallons?
(1) The capacity of the first container is 2 gallons more than the capacity of the second container.
Step 1: Fill the first container to brim.
Step 2: Pour its water into second container till it is full.
Step 3: Now leftover water in first container is 2 gallons. You pour this 2 gallons in third container.
Step 4: Empty second container and repeat steps 1 and 2.
You now have 4 gallons, 2 gallons in third container and 2 gallons in first container.
The problem in a data sufficiency question is that you cannot assume that the third container can hold 2 gallons. What if its capacity is only 1 gallon? Where do you put the 2 gallons of water then? This makes statement 1 alone INSUFFICIENT.
(2) The capacity of the second container is 2 gallons more than the capacity of the third container.
This statement alone is exactly like statement 1 alone. Just that the containers are different but the case is exactly the same. This makes statement 2 alone INSUFFICIENT.
Using both, we now know that capacity of first container is 4 gallons more than the capacity of third container. Now all you have to do is fill first container and pour its water in third container till it fills up. Whatever is left in first container is 4 gallons.
Answer (C)