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# desert outpost has a water supply that is sufficient

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desert outpost has a water supply that is sufficient [#permalink]  18 Jan 2016, 02:29
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Question Stats:

86% (01:27) correct 13% (01:48) wrong based on 36 sessions
A desert outpost has a water supply that is sufficient to last 21 days for 15 people. At the same average rate of water consumption per person, how many days would the water supply last for 9 people?

A 28.0

B 32.5

C 35.0

D 37.5

E 42.0

Practice Questions
Question: 25
Page: 336
Difficulty: medium
[Reveal] Spoiler: OA

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Re: desert outpost has a water supply that is sufficient [#permalink]  18 Jan 2016, 04:54
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Solution

The water supply is enough for 15 people to survive 21 days. Assuming the same average rate of water consumption per person, 1 person would have enough
water to last for (15)(21)=315 days. Therefore, 9 people would have enough water for $$\frac{1}{9}$$ of the 315 days, or 35 days. The correct answer is Choice C.
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Re: desert outpost has a water supply that is sufficient [#permalink]  17 May 2018, 05:56
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Expert's post
sandy wrote:
A desert outpost has a water supply that is sufficient to last 21 days for 15 people. At the same average rate of water consumption per person, how many
days would the water supply last for 9 people?

A 28.0
B 32.5
C 35.0
D 37.5
E 42.0

Let's assign a "nice value" to the amount of water that's available.
Let's first day that each person drinks 1 liter of water EACH DAY.
At that rate, the 15 people would drink a total of 15 liters EACH DAY.
So, in 21 days, they'd drink a total of 315 liters [since (15)(21) = 315].

Now let's see how long that 315 liters of water will last if there are only 9 people.
If each person drinks 1 liter of water EACH DAY, then the 9 people would drink a total of 9 liters EACH DAY.
So, the number of days it takes to drink all 315 = 315/9 = 35

Cheers,
Brent
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Re: desert outpost has a water supply that is sufficient [#permalink]  05 May 2019, 03:30
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sandy wrote:
A desert outpost has a water supply that is sufficient to last 21 days for 15 people. At the same average rate of water consumption per person, how many
days would the water supply last for 9 people?

A 28.0
B 32.5
C 35.0
D 37.5
E 42.0

Practice Questions
Question: 25
Page: 336
Difficulty: medium

Let's say the number of days required by 9 people be = x days

We can infer

$$9 * x = 15 * 21$$ ( 15*21 = the total consumption)

or $$x$$ = $$\frac{{15*21}}{9}$$ = 35 days
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Re: desert outpost has a water supply that is sufficient [#permalink]  28 May 2019, 16:44
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Expert's post
sandy wrote:
A desert outpost has a water supply that is sufficient to last 21 days for 15 people. At the same average rate of water consumption per person, how many
days would the water supply last for 9 people?

A 28.0
B 32.5
C 35.0
D 37.5
E 42.0

If we assume that a person consumes 1 gallon of water per day, then there must be 21 x 15 = 315 gallons of water for the 15 people to last 21 days. If there are 9 people, the 315 gallons of water will last 315/9 = 35 days.

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Re: desert outpost has a water supply that is sufficient [#permalink]  12 Aug 2019, 15:49
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Assuming one gallon is used per person per day is a quick accurate way to solve this problem.
I was curious if it could be solved using dimensional analysis (cancelling units), and I was unsure of how to deal with multiple "pers"; that is, gallons per person per day. I also wanted to see if I could solve the problem using k as a constant, instead of plugging in a number.

My conclusion is that multiple "pers" go on the same line (maybe everyone else already knew this, or maybe there were some people like me, who didn't know it, as it doesn't come up very often), and it can be solved with dimensional analysis.

You can see my exploration of this topic and solving this problem in the attached file.
Attachments

daum_equation_1565653208063.png [ 440.1 KiB | Viewed 1997 times ]

Re: desert outpost has a water supply that is sufficient   [#permalink] 12 Aug 2019, 15:49
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