During ten months of each year, the regulated water supply to Bo's

Question

During ten months of each year, the regulated water supply to Bo's apartment is available only for two hours each night while the family is asleep, with unlimited water flow available during that period. The water is stored in two tanks—in the loft above the bathroom and kitchen—for use when needed. Bo plans to replace the inadequate current tanks with larger ones. Bo's family needs about 300 gallons of water a day—all used during times when no water is flowing from the external supply. The 150- and 300-gallon water tanks cost $300 and $600, respectively, with a buy-one-get-one-free offer on each tank. Which tank or combination of tanks would fulfill the family's needs while minimizing the cost?

(1) The buy-one-get-one-free offer on the water tanks is available only for a month.
(2) During the two hot months of each year, water is supplied to Bo's apartment only on alternate days for two hours while the family is sleeping.

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(1) The buy-one-get-one-free offer on the water tanks is available only for a month.
(2) During the two hot months of each year, water is supplied to Bo's apartment only on alternate days for two hours while the family is sleeping.

happyghost · Answer

If water is available every night, the family needs  300 gal/day , so one 150-gal purchase (get one free) gives  2×150 = 300 gal  for  $300  — cheapest. 
 Statement (2) (alternate-day supply during two hot months) raises the requirement to  600 gal , and the cheapest way then is a single 300-gal purchase (get one free) or two 150-purchases (with freebies) — both cost  $600 .  
Statement (1) (BOGO only for a month) doesn’t tell us anything, so it’s insufficient. 
Statement (2) alone fixes the required capacity and thus the minimal cost — sufficient.

Ramsha12 · Answer

I am convinced with (2) but if we have to minimize the cost then we have to consider the offer as well. Kindly explain what i am missing in this question?

happyghost · Answer

(1) says the offer is available only for a month — but  it doesn't tell us whether Bo will buy within that month or after .
So with (1) alone:
 
 Bo might buy during the month → BOGO applies → costs are low. 
 Bo might buy after the month → BOGO doesn’t apply → costs are higher.  
Two different possible minimum costs ⇒  not sufficient .

Nidhibatra · Answer

can someone please explain this question clearly

glagad · Answer

So, I kinda went on a tangent when I got this question in the exam - I thought, "what if the 300gal tankers don't fit in the given space". In such a case, it should be E (since we don't have any information on the space where they are going to be fit)

If anyone has any thoughts on the same, would love to hear, additionally any guidelines on not drifting on a tangent while solving such DS questions.

If anyone has any thoughts on the same, would love to hear, additionally any guidelines on not drifting on a tangent while solving such DS questions.

arushi118 · Answer

We have to find that which statement will be sufficient to answer that which tank or combination of tanks should Bo buy to optimize cost and fulfill the requirement if her family.

Statement 1 is not enough as we are not told if Bo will buy the tank in the month when the buy-one-get-one offer is available. Cause if she buys during that specific month, then she should buy yhr 150 gallon tank -> as she will get two of them for $300 and those will also satisfy her requirement.
But if she buys in a month when the offer is not available, then she will either have to buy two 150 gallon tanks or one 300 gallon tank -> Both these options will cost her $600. So no way to decide.
Hence, 1 not sufficient.

Statement 2: This tells us that she needs 600 gallons of water when the water is available -> this is only possible with two 300 gallon tanks as there are only 2 spaces for the tanks. Hence, sufficient.

SethTestCrackers · Answer

I'd Like To Nominate This For The Most BS DS Question of All Time

I will walk through what appears to be the logic of the question writer, but it is pretty far from air-tight and though I generally find the editing of official questions to be quite good, this one really stands out. I’d discourage anyone from reading too much into the standard that this question sets.

The Situation 
   Feel free to ignore all of the concerns raised in italics if you're just looking for an explanation to the official answer to this question--but for everyone out there feeling very frustrated by this question, I hear you and I think that you've got a point!

We are told that: 
  "During ten months of each year, the regulated water supply to Bo's apartment is available only for two hours each night while the family is asleep, with unlimited water flow available during that period.”   
 This leaves open what happens during the other two months, so we'll likely need to address that later. 
  It also fails to address whether any other supply besides the "regulated water supply” might be available (unregulated water supply? jugs? rainwater collection?)

Also, though I admit this complaint is clearly outside of scope for the GMAT,     I'm concerned about the physics of this.To actually have "unlimited water flow available" during a "limited" 2 hour period, this problem requires water that flows at an "unlimited" rate. I imagine the universe collapsing into a black hole caused by the density of squeezing "unlimited" water through “limited” plumbing, and it provides a decent visual for the way this entire question makes my brain explode with frustration!

"The water is stored in two tanks—in the loft above the bathroom and kitchen—for use when needed."   
  Nothing states how much space is available for the tanks. So are we supposed to assume that he could have an "unlimited" number of tanks if he wanted? Or that he can only have 2 tanks, but of any size?

"Bo plans to replace the inadequate current tanks with larger ones. Bo's family needs about 300 gallons of water a day—all used during times when no water is flowing from the external supply."  
 This seems intended to tell us not to worry about how his needs might be changed if water is sometimes flowing in and out of the tanks at the same time.

But there are other issues that it raises. Is it reasonable to assume that we should interpret "about 300 gallons" as meaning exactly 300 gallons, every day? Typically it would not seem reasonable to make this jump. If it is an approximate figure and his family actually requires slightly more (308 gallons, for example), then 300 gallons of storage is insufficient. But if the actual daily need is a bit smaller than the approximate figure (292 gallons, for example) and was rounded up to 300, then 300 gallons of storage is adequate. And if his family’s use actually fluctuates daily with unknown high and low values but simply averages “about 300”, then we have no way of knowing how much storage he needs.

Furthermore, nothing states how the family's needs for "about 300 gallons of water" are distributed between the     kitchen and the bathroom, or whether multiple tanks can share that total demand or whether each tank must be connected to and used exclusively in a particular room. If the demand is 150 gallons / day EACH in the bathroom and in the kitchen, that is very different than if the demand is 5 gallons / day in the kitchen and 295 gallons / day in the bathroom (don't judge Bo!). Again, this could have an enormous impact on what configuration of tanks would meet Bo's family's needs.

"    The 150- and 300-gallon water tanks cost $300 and $600, respectively, with a buy-one-get-one-free offer on each tank."

This is a strange use of the word "the" since this is the first time these tanks are mentioned. But it seems we are supposed to assume that Bo's only options are the $300 BOGO 150 gallon tank--so $300 for 2 tanks with 300 total gallons of capacity--and the $600 BOGO 300 gallon tank--so $600 for 2 tanks with 600 total gallons of capacity. In either case, he would spend $1/gallon of tank size.

The question:     "Which tank or combination of tanks would fulfill the family's needs while minimizing the cost?"

To answer this, we need to resolve a two main things: 
  "the family's needs" 
 If we ignore the uncertainty I mentioned above, we do know that they need “about 300” gallons per day for 10 months of the year, but we still don't know what his family's access to water is outside of the 10 months referenced above--ie in the other two months of the year.

"while minimizing costs" 
 This is a bit odd because there is no difference in cost per gallon of storage in either option listed, so really we just need to determine whether 300 gallons (for $300, in the form of purchasing a 150 gallon tank and receiving and a second 150 gallon tank free) would "fulfill the family's needs" (and thus minimize the cost), or whether Bo would instead need to spend $600 for 600 gallons of capacity (in the form of purchasing a 300 gallon tank and receiving and a second 300 gallon tank free) in order to "minimize his cost".

Given the lack of information about space available to fit into, I see no reason why we should consider a third option in which he would buy two 150-gallon tanks/get two free and have the same capacity (600 gallons) for the same price ($600) as the 300-gallon deal, or a fourth option in which he mixes and matches. Perhaps we are expected to assume that there is a limit of 1 per customer, and that he cannot have anyone in his family come and get the deal as well, but something about this question just makes it really difficult to determine where such a line should be drawn.   
 
  But let's stop here and suspend disbelief for a moment.

Statement (1)    
  The buy-one-get-one-free offer on the water tanks is available only for a month.

Though this is probably a good business move from the water tank store, as it will potentially encourage Bo to make a purchase quickly so that he can take advantage of the sale, it does absolutely nothing to resolve the uncertainty around how much capacity Bo needs. 
  Statement (1), on its own, is insufficient. Strike  AD  out, we're looking at BCE.

Statement (2)    
  During the two hot months of each year, water is supplied to Bo's apartment only on alternate days for two hours while the family is sleeping.

Ok, it is tempting to immediately accept this as resolving the biggest issue here–the other months of the year. But is it adequately clear that the “two hot months” are not among the 10 months that were already discussed? Given that this statement tells us that "During the two hot months of each year, water is supplied to Bo's apartment only on alternate days" and we are told above that "During ten months of each year, the regulated water supply to Bo's apartment is available only for two hours each night", we can reasonably infer that, since water cannot be simultaneously available “only on alternate days” and “for two hours each night”, it must be that this is telling us the missing information about the water supply availability during the 2 months for which we previously did not know demand.  This is actually the one part of this question that I have no complaints about at all.

Given that, and given that his tank(s) must now provide 600 gallons (to cover his family’s needs from one moment of water supply until the next one two days later, it is clear that 300 gallons of capacity are NOT enough to cover “about 300” + “about 300” gallons or “about 600 gallons”, so Bo needs to get the two 300-gallon tanks. Given that we only had two options listed  (and if we ignore all of the giant holes in this story),  this leads us to one and only one option for “the tank or combination of tanks would fulfill the family's needs while minimizing the cost” and therefore  Statement 2, on its own, is sufficient and thus The Official Answer to this question is B.

But Let’s Be Clear about Why This is Basically Total BS:  
    If demand is slightly over 300 gallons per day but still "about 300", those 2 tanks will be insufficient (for example, 608 gallons of need would be most effectively served by 5 150 gallon tanks (buy 3 for $900, get 3 free, throw out or resell one if you want since 750 gallons of storage would be adequate, and cheaper than buying 2 300 gallons tanks, getting 2 free, but spending $1200.

Nothing states that the “regulated water” supplied each night is the only or most cost effective means to fill his tanks.  
   Nothing states that the water is "supplied" at a consistent time "on alternate days for two hours while the family is sleeping." So if sometimes it happens at 5 am and sometimes at 11 pm, there could be times when the tanks need to have adequate storage to cover 3 days of water use (fill them 5 am on Day 1, provide 300 gallons of water each for Day 1 and Day 2, and then still need 300 more gallons of water to cover Day 3 (if the supply won't arrive until 11 pm at which time everyone is asleep and done using water for the day).  
   Nothing tells us that there are no other tank options, in terms of size or price points for Bo to consider.  
   Nothing addresses the potential for uneven demand between the bathroom and kitchen. If, during the hot months, Bo needs even slightly more for one room, it changes everything. Just 160 gallons / day in the bathroom (and 140 gallons / day in the kitchen) would make our "supply to supply 2 day demand" require 320 gallons of storage (either 2 300 gallon tanks or 3 150 gallon tanks or 1 300 gallon tank and a 150 gallon tank) and the kitchen would need 280 gallons of storage (either 1 300 gallon tank or 2 150 gallon tanks).   
   Nothing in Statement (2) tells us that "unlimited water" is available during the hot summer months, so how can we be certain that he can get enough water during those times? And if we're always supposed to assume that water supply is unlimited, then why do they specify "unlimited" during the other ten months?   
   Statement (2) says "only on alternate days for two hours while the family is sleeping." Do we need to consider his family's sleep schedule? If someone in the family does shift work and thus there are no times at which all family members are sleeping, does he still have water access at all? And even if we assume that the water is delivered at a consistent time (let's say 1 am - 3 am) and his family is always sleeping during that time, what if someone in the family sometimes comes home late and showers at 12:30 am (before the tanks are refilled) and sometimes showers later (right after the refill, at 3:30 am). Bo’s family would still have consistent   daily   usage AND consistent tank refilling time while the family was sleeping BUT inconsistent use from one filling of the tanks to the next and therefore, once again, we cannot assume that any specific “tank or combination of tanks” would be able to “meet that need.”

The list could go on. In short, there are an "unlimited" number of reasons why the answer to this question really should be E. Kind of shocked that GMAC let this one out into the world and really hoping that it isn't representative of a the general quality of the newer "non-quantitative data sufficiency" questions that they are working into the mix.

During ten months of each year, the regulated water supply to Bo's

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During ten months of each year, the regulated water supply to Bo's

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