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Sub 505 Level|   Work and Rate Problems|                  
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Bunuel
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Bunuel
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Hose X fills 1/28 pool in one hour.
Hose Y fills 1/36 pool in one hour.

Combine X and Y will fill 1/28+1/36 pool in our.Say this comes out to be (a/b) pool in one hour.

To fill full pool it will require 1/(a/b) hours which is b/a .

So answer is (D)
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Answer has to be (C).

Rate-work-formula: R*T=W
W = 50,000 liters

Rx = Rate of hose x
Ry = Rate of hose y
Rt = Combined rate of both hoses = Rx + Ry

Question: Given Rt * T = 50,000 what is T?

Statement (1) allows you to calculate Rx: Rx = 50,000/26. But you have no information about Ry. Not sufficient.
Statement (2) allows you to calculate Ry: Ry = 50,000/36. But you have no information about Rx. Not sufficient.

Combined, you can calculate each rate and add them to get Ry. You then can calculate the time T = 50,000/Rt.

You actually do not need to do any of these calculations. Just imagining the requirement in your head (without even writing down anything), you can see quickly that answer is C.

Btw. I feel question is Sub-600 difficulty.
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Hose X fills 1/28 pool in one hour.
Hose Y fills 1/36 pool in one hour.

Combine X and Y will fill 1/28+1/36 pool in our.Say this comes out to be (a/b) pool in one hour.

To fill full pool it will require 1/(a/b) hours which is b/a .

So answer is (D)

Your answer includes "b/a hours", which is a variable. I think the question asks for a specific number of hours.
You need both statements to get that.
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let A be the Hours taken by hose X alone to fill the pool.
Let B be the hours taken by hose Y alone to fill the pool.

So working together the time taken to fill the pool is given by \(\frac{1}{A}+\frac{1}{B}=\frac{1}{T}\)
Where T is the time taken together to fill the pool.

(1) Hose X alone would take 28 hours to fill the pool.
We are given A no info of B insufficient.

(2) Hose Y alone would take 36 hours to fill the pool.
we are given B no info of A insufficient.

1+2

we have both A and B hence we can calculate T using
\(\frac{1}{28}+\frac{1}{36}= \frac{1}{T}\)

Sufficient
Answer C
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One point worth mentioning here is that one actually does not require the value of total amount of work (i.e. 50,000 litres) to answer this question. The way statements I and II are written, whether the total capacity is 50,000 or 10 litres, the answer will be the same.
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Hose X fills 1/28 of the pool in one hour, and Hose Y fills 1/36 of the pool in one hour.

When combined, X and Y together fill \( \frac{1}{28} + \frac{1}{36} \) of the pool in one hour. Simplifying this sum, we get \( \frac{a}{b} \) of the pool per hour.

To fill the entire pool, the time required will be the reciprocal of \( \frac{a}{b} \), which is \( \frac{b}{a} \) hours.

Therefore, the answer is (D).
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